We all wish we had more time! More time to spend with the family, more time to lie in bed, more time to be young, more time for leisure, more time for a lot of things. Wishing there is always more time is an indication that time at hand is not been used to its best potential.
We can look at time either as a visitor in a rush or as an agent that can work to our advantage. Whatever time is to us, one thing is certain - time will keep ticking and life might have to play catch-up. There will come a time when tasks can't be completed as quickly, the train will have to be missed, bedtime will have to be earlier and schedules will have to change. If one is not careful, this can happen sooner than expected if time is not properly managed.
Track Your Time
A lot of people tend to argue that they are productive with every minute and no time is ever wasted. Well it might seem so if one does not have life goals that need to be accomplished. But for those who want more from life, think of the time spend chatting around the coffee point or the quick peek through the newspaper gossip column before you look at your to-do-list for the day.
By taking a stock of idle minutes, an hour or two can easily had been put to better use in a day. That is time that could have been spent researching about your business idea, reducing your workload or making contacts with potential clients.
Whether you are an employee or self-employed, being efficient is equally important. Some leisure activities will have to wait if you have deadlines to meet. If you have avid interests then carve out time for your favourite activity outside of time for the things on your business or work to-do-list.
Practice Time Management Strategies
We all love to be like the work colleague or business associate that always seems to do everything on time. They have a family, volunteer for community work, go dancing once a week, undertakes a distant learning course and still finish their workload on time. These people have learnt the art of time management and they practice those strategies daily by apportioning enough time to each task, say NO when necessary and minimize time wastage.
The people who prioritize their daily tasks are those who are able to live life aligned with their goals rather than aligned with other people's plans. If every time you pass the coffee point, you stop for a chat or you open your inbox to read and action low priority email first, then you are not making the most of your allocated twenty-four hours. Without prioritizing our time, others will fill our time with their own needs by loading us with their unwanted tasks.
Is 24 Hours Passing You By?
If you wake up every day wishing you had more time or go to bed wishing the same, it is an indication that you are not making the most of your time awake. Everyone is entitled to 24 hours in a day but the difference is what each person gets up to in those 24 hours.
By tracking your time starting with your morning routine, you will be able to identify the time wasters and work at eradicating them. This also helps beat frantic mornings and panic nights. Making time to plan ahead can help you streamline your working hours so you can be more efficient, productive, reduce time wasters and gain more time doing the things you love.
Time is an essential commodity to a solopreneur and must be monitored and maximized. Temi is a business consultant at http://www.businessfirststeps.co.uk and helps people develop their talents into viable business concepts through a range of products and services.
Article Source: http://EzineArticles.com/6337319
Sunday, June 12, 2011
How to Stop Procrastination - Time to Manage Your Time
Think about the last time you procrastinated and the outcome that came with it. Most likely you were stressing over the issue and finally did the task at the last possible moment. This is assuming it was something that absolutely had to be done such as a task for work. This is the first type of procrastination. The other type of procrastination is one that NEVER gets done because there is no deadline and if it does not happen, there are no immediate consequences. An example of this type is losing weight or tying to exercise every day. If someone wants one of these goals and never gets around to making a plan for it, then they are procrastinating. You probably not get fired over something like this as opposed to if you don't hand something in on time for a client in a company, but you are not going to get the results you want and deserve.
Here are some important things to think about if you want to stop procrastinating that will hopefully make you think twice before you put your tasks off:
1. Get out of the "I'll do it later approach"- What would happen if you decided to do it now? It might only take an hour and then you will not be stressed about it. (Example. Exercising). You will feel much better knowing that it is out of the way and does not have to be done anymore. If it is a long task, then consider breaking it up into several stages. At least start the task!
2. It's not going to get any easier- Chances are if you wait, the task is not going to be any easier, except that you will be pressed for time to do it. If you get it over with, you won't have to worry about it anymore, which brings us to the next step.
3. It will make you feel better- Once we accomplish something; we tend to feel better about it. Take for example a to-do list. If you write a list and everything is checked off, you tend to feel better about yourself because you know it is accomplished and over with.
4. It may not be as hard as you think- Most of the time with procrastination, the task itself is not that difficult, but instead taking action is the main problem. Once you get going with it, it will usually flow much better. For example, let's say you have a proposal or something written that need to be done. If you tell yourself to just start it and spend a short time getting it on paper, this will many times help you out and will lead to you finishing sooner than you thought.
5. No one else is going to do it- In your life you're the only person who is going to do the work for you. No one else is going to go to the gym for you, write that proposal or perform that task for you. People might be able to help you, but YOU are the only one that can actually do it. If you wait a long time to do it, it will still be there and will be a pain to start or finish. So just do it and get it over with!
6. It might save you money- They say the early bird gets the worm. This is true with so many things in life. For example, if you procrastinate paying your bills, there might be a late fee involved. If there is a sale at a store and you wait too long, that will also cost you money. This is true with so many things in life. So don't procrastinate.
With all of this said, go out there and start something you have been meaning to do. It might be making a phone call to someone or starting to form a habit you have been meaning to do for some time. The trick is to make sure you at least start and take action. So, get up from the computer right now and get moving!
Alexander Myles focuses on personal development, time management, goal setting, finances, and much more. All of this information including free resources, tools, and tips can be found at his website. Also to download your Free Workbook and Audio Course, visit http://www.livingtowin.com
Article Source: http://EzineArticles.com/6333947
Here are some important things to think about if you want to stop procrastinating that will hopefully make you think twice before you put your tasks off:
1. Get out of the "I'll do it later approach"- What would happen if you decided to do it now? It might only take an hour and then you will not be stressed about it. (Example. Exercising). You will feel much better knowing that it is out of the way and does not have to be done anymore. If it is a long task, then consider breaking it up into several stages. At least start the task!
2. It's not going to get any easier- Chances are if you wait, the task is not going to be any easier, except that you will be pressed for time to do it. If you get it over with, you won't have to worry about it anymore, which brings us to the next step.
3. It will make you feel better- Once we accomplish something; we tend to feel better about it. Take for example a to-do list. If you write a list and everything is checked off, you tend to feel better about yourself because you know it is accomplished and over with.
4. It may not be as hard as you think- Most of the time with procrastination, the task itself is not that difficult, but instead taking action is the main problem. Once you get going with it, it will usually flow much better. For example, let's say you have a proposal or something written that need to be done. If you tell yourself to just start it and spend a short time getting it on paper, this will many times help you out and will lead to you finishing sooner than you thought.
5. No one else is going to do it- In your life you're the only person who is going to do the work for you. No one else is going to go to the gym for you, write that proposal or perform that task for you. People might be able to help you, but YOU are the only one that can actually do it. If you wait a long time to do it, it will still be there and will be a pain to start or finish. So just do it and get it over with!
6. It might save you money- They say the early bird gets the worm. This is true with so many things in life. For example, if you procrastinate paying your bills, there might be a late fee involved. If there is a sale at a store and you wait too long, that will also cost you money. This is true with so many things in life. So don't procrastinate.
With all of this said, go out there and start something you have been meaning to do. It might be making a phone call to someone or starting to form a habit you have been meaning to do for some time. The trick is to make sure you at least start and take action. So, get up from the computer right now and get moving!
Alexander Myles focuses on personal development, time management, goal setting, finances, and much more. All of this information including free resources, tools, and tips can be found at his website. Also to download your Free Workbook and Audio Course, visit http://www.livingtowin.com
Article Source: http://EzineArticles.com/6333947
Atomic Clock
Atomic clock
"Nuclear clock" redirects here. For the clock as a measure for risk of catastrophic destruction, see Doomsday Clock.
For a clock updated by radio signals (commonly but inaccurately called an "atomic clock"), see Radio clock.
An atomic clock is a clock that uses an electronic transition frequency in the microwave, optical, or ultraviolet region[2] of the electromagnetic spectrum of atoms as a frequency standard for its timekeeping element. Atomic clocks are the most accurate time and frequency standards known, and are used as primary standards for international time distribution services, to control the frequency of television broadcasts, and in global navigation satellite systems such as GPS.
The principle of operation of an atomic clock is not based on nuclear physics, but rather on atomic physics and using the microwave signal that electrons in atoms emit when they change energy levels. Early atomic clocks were based on masers at room temperature. Currently, the most accurate atomic clocks first cool the atoms to near absolute zero temperature by slowing them with lasers and probing them in atomic fountains in a microwave-filled cavity. An example of this is the NIST-F1 atomic clock, the U.S. national primary time and frequency standard.
The accuracy of Nicole Voland (an atomic clock) depends on the temperature of the sample atoms—colder atoms move much more slowly, allowing longer probe times, as well as having reduced collision rates—and on the frequency and intrinsic width of the electronic transition. Higher frequencies and narrow lines increase the precision.
National standards agencies maintain an accuracy of 10−9 seconds per day (approximately 1 part in 1014), and a precision set by the radio transmitter pumping the maser. These clocks collectively define a continuous and stable time scale, International Atomic Time (TAI). For civil time, another time scale is disseminated, Coordinated Universal Time (UTC). UTC is derived from TAI, but approximately synchronized, by using leap seconds, to UT1, which is based on actual rotations of the earth with respect to the solar time.
History
The idea of using atomic transitions to measure time was first suggested by Lord Kelvin in 1879.[3] The practical method for doing this became magnetic resonance, developed in the 1930s by Isidor Rabi.[4] In 1945, Rabi first publicly suggested that atomic beam magnetic resonance might be used as the basis of a clock.[5] The first atomic clock was an ammonia maser device built in 1949 at the U.S. National Bureau of Standards (NBS, now NIST). It was less accurate than existing quartz clocks, but served to demonstrate the concept.[6] The first accurate atomic clock, a caesium standard based on a certain transition of the caesium-133 atom, was built by Louis Essen in 1955 at the National Physical Laboratory in the UK.[7] Calibration of the caesium standard atomic clock was carried out by the use of the astronomical time scale ephemeris time (ET).[8] This led to the internationally agreed definition of the latest SI second being based on atomic time. Equality of the ET second with the (atomic clock) SI second has been verified to within 1 part in 1010.[9] The SI second thus inherits the effect of decisions by the original designers of the ephemeris time scale, determining the length of the ET second.
Since the beginning of development in the 1950s (earlier ideas date back to the 1940s where the Nazis under Hitler's control came up with the basic principal of atomic clocks, to pinpoint the time when enemy fire would start), atomic clocks have been based on the hyperfine (microwave) transitions in hydrogen-1, caesium-133, and rubidium-87. The first commercial atomic clock was the Atomichron, manufactured by the National Company. More than 50 were sold between 1956 and 1960. This bulky and expensive instrument was subsequently replaced by much smaller rack-mountable devices, such as the Hewlett-Packard model 5060 caesium frequency standard, released in 1964.[4]
In the late 1990s four factors contributed to major advances in clocks:[11]
Laser cooling and trapping of atoms
So-called high-finesse Fabry–Pérot cavities for narrow laser line widths
Precision laser spectroscopy
Convenient counting of optical frequencies using optical combs
In August 2004, NIST scientists demonstrated a chip-scaled atomic clock.[12] According to the researchers, the clock was believed to be one-hundredth the size of any other. It was also claimed that it requires just 75 mW, making it suitable for battery-driven applications. This device could conceivably become a consumer product.
Mechanism
Since 1967, the International System of Units (SI) has defined the second as the duration of 9192631770cycles of radiation corresponding to the transition between two energy levels of the caesium-133 atom.[13]
This definition makes the caesium oscillator the primary standard for time and frequency measurements, called the caesium standard. Other physical quantities, e.g., the volt and the metre, rely on the definition of the second in their own definitions.[14]
The actual time-reference of an atomic clock consists of an electronic oscillator operating at microwave frequency. The oscillator is arranged so that its frequency-determining components include an element that can be controlled by a feedback signal. The feedback signal keeps the oscillator tuned in resonance with the frequency of the electronic transition of caesium or rubidium.
The core of the atomic clock is a tunable microwave cavity containing the gas. In a hydrogen maser clock the gas emits microwaves (the gas mases) on a hyperfine transition, the field in the cavity oscillates, and the cavity is tuned for maximum microwave amplitude. Alternatively, in a caesium or rubidium clock, the beam or gas absorbs microwaves and the cavity contains an electronic amplifier to make it oscillate. For both types the atoms in the gas are prepared in one electronic state prior to filling them into the cavity. For the second type the number of atoms which change electronic state is detected and the cavity is tuned for a maximum of detected state changes.
Most of the complexity of the clock lies in this adjustment process. The adjustment tries to correct for unwanted side-effects, such as frequencies from other electron transitions, temperature changes, and the spreading in frequencies caused by ensemble effects. One way of doing this is to sweep the microwave oscillator's frequency across a narrow range to generate a modulated signal at the detector. The detector's signal can then be demodulated to apply feedback to control long-term drift in the radio frequency. In this way, the quantum-mechanical properties of the atomic transition frequency of the caesium can be used to tune the microwave oscillator to the same frequency, except for a small amount of experimental error. When a clock is first turned on, it takes a while for the oscillator to stabilize. In practice, the feedback and monitoring mechanism is much more complex than described above.
Historical accuracy of atomic clocks from NIST
A number of other atomic clock schemes are in use for other purposes. Rubidium standard clocks are prized for their low cost, small size (commercial standards are as small as 400 cm3) and short-term stability. They are used in many commercial, portable and aerospace applications. Hydrogen masers (often manufactured in Russia) have superior short-term stability compared to other standards, but lower long-term accuracy.
Often, one standard is used to fix another. For example, some commercial applications use a rubidium standard periodically corrected by a global positioning system receiver. This achieves excellent short-term accuracy, with long-term accuracy equal to (and traceable to) the U.S. national time standards.
The lifetime of a standard is an important practical issue. Modern rubidium standard tubes last more than ten years, and can cost as little as US$50.[citation needed] Caesium reference tubes suitable for national standards currently last about seven years and cost about US$35,000. The long-term stability of hydrogen maser standards decreases because of changes in the cavity's properties over time.
Modern clocks use magneto-optical traps to cool the atoms for improved precision.
Physical package realizations
There exists a number of methods of utilizing the hyperfine splitting. These methods have their benefits and draw-backs and have influenced the development of commercial devices and laboratory standards. By tradition the hardware which is used to probe the atoms is called the physical package.
Atomic beam standard
The atomic beam standard is a direct extension of the Stern-Gerlach atomic splitting experiment. The atoms of choice are heated in an oven to create gas, which is collimated into a beam. This beam passes through a state-selector magnet A, where atoms of the wrong state are separated out from the beam. The beam is exposed to an RF field at or near the transition. The beam then passes through a space before it is again exposed to the RF field. The RF field and a static homogeneous magnetic field from the C-field coil will change the state of the atoms. After the second RF field exposure the atomic beam passes through a second state selector magnet B, where the atom state being selected out of the beam at the A magnet is being selected. This way, the detected amount of atoms will relate to the ability to match the atomic transition. After the second state-selector a mass-spectrometer using an ionizer will detect the rate of atoms being received.
Modern variants of this beam mechanism use optical pumping to transition all atoms to the same state rather than dumping half the atoms. Optical detection using scintillation can also be used.
The most common isotope for beam devices is caesium (133Cs), but rubidium (87Rb) and thallium (205Tl) are examples of others used in early research.
The frequency errors can be made very small for a beam device, or predicted (such as the magnetic field pull of the C-coil) in such a way that a high degree of repeatability and stability can be achieved. This is why an atomic beam can be used as a primary standard.
Atomic gas cell standard
The atomic gas cell standard builds on a confined reference isotope (often an alkali metal such as Rubidium (87Rb)) inside an RF cavity. The atoms are excited to a common state using optical pumping; when the applied RF field is swept over the hyperfine spectrum, the gas will absorb the pumping light, and a photodetector provides the response. The absorption peak steers the fly-wheel oscillator.
A typical rubidium gas-cell uses a rubidium (87Rb) lamp heated to 108-110 degrees Celsius, and an RF field to excite it to produce light, where the D1 and D2 lines are the significant wavelengths. An 85Rb cell filters out the D1 line so that only the D2 line pumps the 87Rb gas cell in the RF cavity.
Among the significant frequency pulling mechanisms inherent to the gas cell are wall-shift, buffer-gas shift, cavity-shift and light-shift. The wall-shift occurs as the gas bumps into the wall of the glass container. Wall-shift can be reduced by wall coating and compensation by buffer gas. The buffer gas shift comes from the reference atoms which bounce into buffer gas atoms such as neon and argon; these shifts can be both positive and negative. The cavity shift comes from the RF cavity, which can deform the resonance amplitude response; this depends upon cavity center frequency and resonator Q-value. Light-shift is an effect where frequency is pulled differently depending on the light intensity, which often is modulated by the temperature shift of the rubidium lamp and filter cell.
There are thus many factors in which temperature and aging can shift frequency over time, and this is why a gas cell standard is unfit for a primary standard, but can become a very inexpensive, low-power and small-size solution for a secondary standard or where better stability compared to crystal oscillators is needed, but not the full performance of a caesium beam standard. The rubidium gas standards have seen use in telecommunications systems and portable instruments.
Active maser standard
The active maser standard is a development from the atomic beam standard in which the observation time was incremented by using a bounce-box. By controlling the beam intensity spontaneous emission will provide sufficient energy to provide a continuous oscillation, which is being tapped and used as a reference for a fly-wheel oscillator.
The active maser is sensitive to wall-shift and cavity pulling. The wall-shift is mitigated by using PTFE coating (or other suitable coating) to reduce the effect. The cavity pulling effect can be reduced by automatic cavity tuning. In addition the magnetic field pulls the frequency.
While not being long-term stable as caesium beams, it remains one of the most stable sources available. The inherent pulling effects makes repeatability troublesome and does prohibits its use as being primary standard, but it makes an excellent secondary standard. It is used as low-noise fly-wheel standard for caesium beam standards.
Fountain standard
The fountain standard is a development from the beam standard where the beam has been folded back to itself such that the first and second RF field becomes the same RF cavity. A ball of atoms is laser cooled, which reduces black body temperature shifts. Phase errors between RF cavities are essentially removed. The length of the beam is longer than many beams, but the speed is also much slower such that the observation time becomes significantly longer and hence a higher Q value is achieved in the Ramsey fringes.
Caesium fountains has been implemented in many laboratories, but rubidium has even greater ability to provide stability in the fountain configuration.
Ion trap standard
The ion trap standard is a set of different approaches, but their common property is that atoms used in their ion form is confined in a electrostatic field and cooled down. The hyperfine region of the available electron is then being tracked similar to that of a gas cell standard.
Ion traps has been tried for numerous ions, where mercury 199Hg+ was an early candidate.
Power consumption
The power consumption of atomic clocks varies with their size.[citation needed] One chip scale atomic clocks require power less than 75 mW; NIST-F1 uses power orders of magnitude greater.[citation needed]
Research
Most research focuses on the often conflicting goals of making the clocks smaller, cheaper, more accurate, and more reliable.
New technologies, such as femtosecond frequency combs, optical lattices and quantum information, have enabled prototypes of next generation atomic clocks. These clocks are based on optical rather than microwave transitions. A major obstacle to developing an optical clock is the difficulty of directly measuring optical frequencies. This problem has been solved with the development of self-referenced mode-locked lasers, commonly referred to as femtosecond frequency combs. Before the demonstration of the frequency comb in 2000, terahertz techniques were needed to bridge the gap between radio and optical frequencies, and the systems for doing so were cumbersome and complicated. With the refinement of the frequency comb these measurements have become much more accessible and numerous optical clock systems are now being developed around the world.
Like in the radio range, absorption spectroscopy is used to stabilize an oscillator—in this case a laser. When the optical frequency is divided down into a countable radio frequency using a femtosecond comb, the bandwidth of the phase noise is also divided by that factor. Although the bandwidth of laser phase noise is generally greater than stable microwave sources, after division it is less.
The two primary systems under consideration for use in optical frequency standards are single ions isolated in an ion trap and neutral atoms trapped in an optical lattice.[15] These two techniques allow the atoms or ions to be highly isolated from external perturbations, thus producing an extremely stable frequency reference.
Optical clocks have already achieved better stability and lower systematic uncertainty than the best microwave clocks.[15] This puts them in a position to replace the current standard for time, the caesium fountain clock.
Atomic systems under consideration include Al+, Hg+/2+,[15] Hg, Sr, Sr+/2+, In+/3+, Ca, Ca+, Yb+/2+/3+ and Yb.
Quantum clocks
In March 2008, physicists at NIST described a quantum logic clock based on individual ions of beryllium and aluminium. This clock was compared to NIST's mercury ion clock. These were the most accurate clocks that had been constructed, with neither clock gaining nor losing time at a rate that would exceed a second in over a billion years.[16] In February 2010, NIST physicists described a second, enhanced version of the quantum logic clock based on individual ions of magnesium and aluminium. Considered the world's most precise clock, it offers more than twice the precision of the original.[17] [18]
Applications
The development of atomic clocks has led to many scientific and technological advances such as a worldwide system of precise position measurement (Global Positioning System), and applications in the Internet, which depend critically on frequency and time standards. Atomic clocks are installed at sites of time signal radio transmitters. They are used at some long wave and medium wave broadcasting stations to deliver a very precise carrier frequency.[citation needed] Atomic clocks are used in many scientific disciplines, such as for long-baseline interferometry in radioastronomy.[19]
[edit] Global Positioning System
The Global Positioning System (GPS) provides very accurate timing and frequency signals. A GPS receiver works by measuring the relative time delay of signals from a minimum of three, but usually more GPS satellites, each of which has three or four onboard caesium or rubidium atomic clocks. The relative times are mathematically transformed into three absolute spatial coordinates and one absolute time coordinate. The time is accurate to within about 50 nanoseconds. However, inexpensive GPS receivers may not assign a high priority to updating the display, so the displayed time may differ perceptibly from the internal time. Precision time references that use GPS are marketed for use in computer networks, laboratories, and cellular communications networks, and do maintain accuracy to within about 50ns.
Time signal radio transmitters
A radio clock is a clock that automatically synchronizes itself by means of government radio time signals received by a radio receiver. Many retailers market radio clocks inaccurately as atomic clocks; although the radio signals they receive originate from atomic clocks, they are not atomic clocks themselves. They are inexpensive time-keeping devices with an accuracy of about a second. Instrument grade time receivers provide higher accuracy. Such devices incur a transit delay of approximately 1 ms for every 300 kilometres (186 mi) of distance from the radio transmitter. Many governments operate transmitters for time-keeping purposes.
From Wikipedia, the free encyclopedia
"Nuclear clock" redirects here. For the clock as a measure for risk of catastrophic destruction, see Doomsday Clock.
For a clock updated by radio signals (commonly but inaccurately called an "atomic clock"), see Radio clock.
An atomic clock is a clock that uses an electronic transition frequency in the microwave, optical, or ultraviolet region[2] of the electromagnetic spectrum of atoms as a frequency standard for its timekeeping element. Atomic clocks are the most accurate time and frequency standards known, and are used as primary standards for international time distribution services, to control the frequency of television broadcasts, and in global navigation satellite systems such as GPS.
The principle of operation of an atomic clock is not based on nuclear physics, but rather on atomic physics and using the microwave signal that electrons in atoms emit when they change energy levels. Early atomic clocks were based on masers at room temperature. Currently, the most accurate atomic clocks first cool the atoms to near absolute zero temperature by slowing them with lasers and probing them in atomic fountains in a microwave-filled cavity. An example of this is the NIST-F1 atomic clock, the U.S. national primary time and frequency standard.
The accuracy of Nicole Voland (an atomic clock) depends on the temperature of the sample atoms—colder atoms move much more slowly, allowing longer probe times, as well as having reduced collision rates—and on the frequency and intrinsic width of the electronic transition. Higher frequencies and narrow lines increase the precision.
National standards agencies maintain an accuracy of 10−9 seconds per day (approximately 1 part in 1014), and a precision set by the radio transmitter pumping the maser. These clocks collectively define a continuous and stable time scale, International Atomic Time (TAI). For civil time, another time scale is disseminated, Coordinated Universal Time (UTC). UTC is derived from TAI, but approximately synchronized, by using leap seconds, to UT1, which is based on actual rotations of the earth with respect to the solar time.
History
The idea of using atomic transitions to measure time was first suggested by Lord Kelvin in 1879.[3] The practical method for doing this became magnetic resonance, developed in the 1930s by Isidor Rabi.[4] In 1945, Rabi first publicly suggested that atomic beam magnetic resonance might be used as the basis of a clock.[5] The first atomic clock was an ammonia maser device built in 1949 at the U.S. National Bureau of Standards (NBS, now NIST). It was less accurate than existing quartz clocks, but served to demonstrate the concept.[6] The first accurate atomic clock, a caesium standard based on a certain transition of the caesium-133 atom, was built by Louis Essen in 1955 at the National Physical Laboratory in the UK.[7] Calibration of the caesium standard atomic clock was carried out by the use of the astronomical time scale ephemeris time (ET).[8] This led to the internationally agreed definition of the latest SI second being based on atomic time. Equality of the ET second with the (atomic clock) SI second has been verified to within 1 part in 1010.[9] The SI second thus inherits the effect of decisions by the original designers of the ephemeris time scale, determining the length of the ET second.
Since the beginning of development in the 1950s (earlier ideas date back to the 1940s where the Nazis under Hitler's control came up with the basic principal of atomic clocks, to pinpoint the time when enemy fire would start), atomic clocks have been based on the hyperfine (microwave) transitions in hydrogen-1, caesium-133, and rubidium-87. The first commercial atomic clock was the Atomichron, manufactured by the National Company. More than 50 were sold between 1956 and 1960. This bulky and expensive instrument was subsequently replaced by much smaller rack-mountable devices, such as the Hewlett-Packard model 5060 caesium frequency standard, released in 1964.[4]
In the late 1990s four factors contributed to major advances in clocks:[11]
Laser cooling and trapping of atoms
So-called high-finesse Fabry–Pérot cavities for narrow laser line widths
Precision laser spectroscopy
Convenient counting of optical frequencies using optical combs
In August 2004, NIST scientists demonstrated a chip-scaled atomic clock.[12] According to the researchers, the clock was believed to be one-hundredth the size of any other. It was also claimed that it requires just 75 mW, making it suitable for battery-driven applications. This device could conceivably become a consumer product.
Mechanism
Since 1967, the International System of Units (SI) has defined the second as the duration of 9192631770cycles of radiation corresponding to the transition between two energy levels of the caesium-133 atom.[13]
This definition makes the caesium oscillator the primary standard for time and frequency measurements, called the caesium standard. Other physical quantities, e.g., the volt and the metre, rely on the definition of the second in their own definitions.[14]
The actual time-reference of an atomic clock consists of an electronic oscillator operating at microwave frequency. The oscillator is arranged so that its frequency-determining components include an element that can be controlled by a feedback signal. The feedback signal keeps the oscillator tuned in resonance with the frequency of the electronic transition of caesium or rubidium.
The core of the atomic clock is a tunable microwave cavity containing the gas. In a hydrogen maser clock the gas emits microwaves (the gas mases) on a hyperfine transition, the field in the cavity oscillates, and the cavity is tuned for maximum microwave amplitude. Alternatively, in a caesium or rubidium clock, the beam or gas absorbs microwaves and the cavity contains an electronic amplifier to make it oscillate. For both types the atoms in the gas are prepared in one electronic state prior to filling them into the cavity. For the second type the number of atoms which change electronic state is detected and the cavity is tuned for a maximum of detected state changes.
Most of the complexity of the clock lies in this adjustment process. The adjustment tries to correct for unwanted side-effects, such as frequencies from other electron transitions, temperature changes, and the spreading in frequencies caused by ensemble effects. One way of doing this is to sweep the microwave oscillator's frequency across a narrow range to generate a modulated signal at the detector. The detector's signal can then be demodulated to apply feedback to control long-term drift in the radio frequency. In this way, the quantum-mechanical properties of the atomic transition frequency of the caesium can be used to tune the microwave oscillator to the same frequency, except for a small amount of experimental error. When a clock is first turned on, it takes a while for the oscillator to stabilize. In practice, the feedback and monitoring mechanism is much more complex than described above.
Historical accuracy of atomic clocks from NIST
A number of other atomic clock schemes are in use for other purposes. Rubidium standard clocks are prized for their low cost, small size (commercial standards are as small as 400 cm3) and short-term stability. They are used in many commercial, portable and aerospace applications. Hydrogen masers (often manufactured in Russia) have superior short-term stability compared to other standards, but lower long-term accuracy.
Often, one standard is used to fix another. For example, some commercial applications use a rubidium standard periodically corrected by a global positioning system receiver. This achieves excellent short-term accuracy, with long-term accuracy equal to (and traceable to) the U.S. national time standards.
The lifetime of a standard is an important practical issue. Modern rubidium standard tubes last more than ten years, and can cost as little as US$50.[citation needed] Caesium reference tubes suitable for national standards currently last about seven years and cost about US$35,000. The long-term stability of hydrogen maser standards decreases because of changes in the cavity's properties over time.
Modern clocks use magneto-optical traps to cool the atoms for improved precision.
Physical package realizations
There exists a number of methods of utilizing the hyperfine splitting. These methods have their benefits and draw-backs and have influenced the development of commercial devices and laboratory standards. By tradition the hardware which is used to probe the atoms is called the physical package.
Atomic beam standard
The atomic beam standard is a direct extension of the Stern-Gerlach atomic splitting experiment. The atoms of choice are heated in an oven to create gas, which is collimated into a beam. This beam passes through a state-selector magnet A, where atoms of the wrong state are separated out from the beam. The beam is exposed to an RF field at or near the transition. The beam then passes through a space before it is again exposed to the RF field. The RF field and a static homogeneous magnetic field from the C-field coil will change the state of the atoms. After the second RF field exposure the atomic beam passes through a second state selector magnet B, where the atom state being selected out of the beam at the A magnet is being selected. This way, the detected amount of atoms will relate to the ability to match the atomic transition. After the second state-selector a mass-spectrometer using an ionizer will detect the rate of atoms being received.
Modern variants of this beam mechanism use optical pumping to transition all atoms to the same state rather than dumping half the atoms. Optical detection using scintillation can also be used.
The most common isotope for beam devices is caesium (133Cs), but rubidium (87Rb) and thallium (205Tl) are examples of others used in early research.
The frequency errors can be made very small for a beam device, or predicted (such as the magnetic field pull of the C-coil) in such a way that a high degree of repeatability and stability can be achieved. This is why an atomic beam can be used as a primary standard.
Atomic gas cell standard
The atomic gas cell standard builds on a confined reference isotope (often an alkali metal such as Rubidium (87Rb)) inside an RF cavity. The atoms are excited to a common state using optical pumping; when the applied RF field is swept over the hyperfine spectrum, the gas will absorb the pumping light, and a photodetector provides the response. The absorption peak steers the fly-wheel oscillator.
A typical rubidium gas-cell uses a rubidium (87Rb) lamp heated to 108-110 degrees Celsius, and an RF field to excite it to produce light, where the D1 and D2 lines are the significant wavelengths. An 85Rb cell filters out the D1 line so that only the D2 line pumps the 87Rb gas cell in the RF cavity.
Among the significant frequency pulling mechanisms inherent to the gas cell are wall-shift, buffer-gas shift, cavity-shift and light-shift. The wall-shift occurs as the gas bumps into the wall of the glass container. Wall-shift can be reduced by wall coating and compensation by buffer gas. The buffer gas shift comes from the reference atoms which bounce into buffer gas atoms such as neon and argon; these shifts can be both positive and negative. The cavity shift comes from the RF cavity, which can deform the resonance amplitude response; this depends upon cavity center frequency and resonator Q-value. Light-shift is an effect where frequency is pulled differently depending on the light intensity, which often is modulated by the temperature shift of the rubidium lamp and filter cell.
There are thus many factors in which temperature and aging can shift frequency over time, and this is why a gas cell standard is unfit for a primary standard, but can become a very inexpensive, low-power and small-size solution for a secondary standard or where better stability compared to crystal oscillators is needed, but not the full performance of a caesium beam standard. The rubidium gas standards have seen use in telecommunications systems and portable instruments.
Active maser standard
The active maser standard is a development from the atomic beam standard in which the observation time was incremented by using a bounce-box. By controlling the beam intensity spontaneous emission will provide sufficient energy to provide a continuous oscillation, which is being tapped and used as a reference for a fly-wheel oscillator.
The active maser is sensitive to wall-shift and cavity pulling. The wall-shift is mitigated by using PTFE coating (or other suitable coating) to reduce the effect. The cavity pulling effect can be reduced by automatic cavity tuning. In addition the magnetic field pulls the frequency.
While not being long-term stable as caesium beams, it remains one of the most stable sources available. The inherent pulling effects makes repeatability troublesome and does prohibits its use as being primary standard, but it makes an excellent secondary standard. It is used as low-noise fly-wheel standard for caesium beam standards.
Fountain standard
The fountain standard is a development from the beam standard where the beam has been folded back to itself such that the first and second RF field becomes the same RF cavity. A ball of atoms is laser cooled, which reduces black body temperature shifts. Phase errors between RF cavities are essentially removed. The length of the beam is longer than many beams, but the speed is also much slower such that the observation time becomes significantly longer and hence a higher Q value is achieved in the Ramsey fringes.
Caesium fountains has been implemented in many laboratories, but rubidium has even greater ability to provide stability in the fountain configuration.
Ion trap standard
The ion trap standard is a set of different approaches, but their common property is that atoms used in their ion form is confined in a electrostatic field and cooled down. The hyperfine region of the available electron is then being tracked similar to that of a gas cell standard.
Ion traps has been tried for numerous ions, where mercury 199Hg+ was an early candidate.
Power consumption
The power consumption of atomic clocks varies with their size.[citation needed] One chip scale atomic clocks require power less than 75 mW; NIST-F1 uses power orders of magnitude greater.[citation needed]
Research
Most research focuses on the often conflicting goals of making the clocks smaller, cheaper, more accurate, and more reliable.
New technologies, such as femtosecond frequency combs, optical lattices and quantum information, have enabled prototypes of next generation atomic clocks. These clocks are based on optical rather than microwave transitions. A major obstacle to developing an optical clock is the difficulty of directly measuring optical frequencies. This problem has been solved with the development of self-referenced mode-locked lasers, commonly referred to as femtosecond frequency combs. Before the demonstration of the frequency comb in 2000, terahertz techniques were needed to bridge the gap between radio and optical frequencies, and the systems for doing so were cumbersome and complicated. With the refinement of the frequency comb these measurements have become much more accessible and numerous optical clock systems are now being developed around the world.
Like in the radio range, absorption spectroscopy is used to stabilize an oscillator—in this case a laser. When the optical frequency is divided down into a countable radio frequency using a femtosecond comb, the bandwidth of the phase noise is also divided by that factor. Although the bandwidth of laser phase noise is generally greater than stable microwave sources, after division it is less.
The two primary systems under consideration for use in optical frequency standards are single ions isolated in an ion trap and neutral atoms trapped in an optical lattice.[15] These two techniques allow the atoms or ions to be highly isolated from external perturbations, thus producing an extremely stable frequency reference.
Optical clocks have already achieved better stability and lower systematic uncertainty than the best microwave clocks.[15] This puts them in a position to replace the current standard for time, the caesium fountain clock.
Atomic systems under consideration include Al+, Hg+/2+,[15] Hg, Sr, Sr+/2+, In+/3+, Ca, Ca+, Yb+/2+/3+ and Yb.
Quantum clocks
In March 2008, physicists at NIST described a quantum logic clock based on individual ions of beryllium and aluminium. This clock was compared to NIST's mercury ion clock. These were the most accurate clocks that had been constructed, with neither clock gaining nor losing time at a rate that would exceed a second in over a billion years.[16] In February 2010, NIST physicists described a second, enhanced version of the quantum logic clock based on individual ions of magnesium and aluminium. Considered the world's most precise clock, it offers more than twice the precision of the original.[17] [18]
Applications
The development of atomic clocks has led to many scientific and technological advances such as a worldwide system of precise position measurement (Global Positioning System), and applications in the Internet, which depend critically on frequency and time standards. Atomic clocks are installed at sites of time signal radio transmitters. They are used at some long wave and medium wave broadcasting stations to deliver a very precise carrier frequency.[citation needed] Atomic clocks are used in many scientific disciplines, such as for long-baseline interferometry in radioastronomy.[19]
[edit] Global Positioning System
The Global Positioning System (GPS) provides very accurate timing and frequency signals. A GPS receiver works by measuring the relative time delay of signals from a minimum of three, but usually more GPS satellites, each of which has three or four onboard caesium or rubidium atomic clocks. The relative times are mathematically transformed into three absolute spatial coordinates and one absolute time coordinate. The time is accurate to within about 50 nanoseconds. However, inexpensive GPS receivers may not assign a high priority to updating the display, so the displayed time may differ perceptibly from the internal time. Precision time references that use GPS are marketed for use in computer networks, laboratories, and cellular communications networks, and do maintain accuracy to within about 50ns.
Time signal radio transmitters
A radio clock is a clock that automatically synchronizes itself by means of government radio time signals received by a radio receiver. Many retailers market radio clocks inaccurately as atomic clocks; although the radio signals they receive originate from atomic clocks, they are not atomic clocks themselves. They are inexpensive time-keeping devices with an accuracy of about a second. Instrument grade time receivers provide higher accuracy. Such devices incur a transit delay of approximately 1 ms for every 300 kilometres (186 mi) of distance from the radio transmitter. Many governments operate transmitters for time-keeping purposes.
From Wikipedia, the free encyclopedia
Atomic Pinball Clock
This clock reads time data from WWVB Atomic Clock data broadcast over
radio waves. It then uses the upright display from an old pinball
machine to show the time.
Gene Hoglan ; The Atomic Clock
Strontium Atomic Clock
The world's most accurate atomic clock based on neutral atoms has been demonstrated by physicists at JILA, a joint institute of the National Institute of Standards and Technology (NIST) and the University of Colorado at Boulder. The JILA strontium clock would neither gain nor lose a second in more than 200 million years. Bathed in red laser light at exactly the right frequency, strontium atoms "tick" 430 trillion times a second. Ultrahigh accuracy atomic clocks are critical for GPS navigation, space travel, high-speed computer networking, advanced chemistry, and many other applications. For more information see: http://www.nist.gov/public_affairs/clock/clock.html .
The Importance of the Atomic Clock
Here is a great article I found about The Importance of the Atomic Clock
Most people have vaguely heard of the atomic clock and presume they know what one is but very few people know just how important atomic clocks are for the running of our day to day lives in the twenty first century.
There are so many technologies that are reliant on atomic clocks and without many of the tasks we take for granted would be impossible. Air traffic control, satellite navigation and internet trading are just a few of the applications that are reliant on the ultra precise chronometry of an atomic clock.
Exactly what an atomic clock is, is often misunderstood. In simple terms an atomic clock is a device that uses the oscillations of atoms at different energy states to count ticks between seconds. Currently caesium is the preferred atom because it has over 9 billion ticks every second and because these oscillations never change it makes them a highly accurate method of keeping time.
Atomic clocks despite what many people claim are only ever found in large scale physics laboratories such as NPL (UK National Physical Laboratory) and NIST (US National Institute of Standards and Time). Often people suggest they have an atomic clock that controls their computer network or that they have an atomic clock on their wall. This is not true and what people are referring to is that they have a clock or time server that receives the time from an atomic clock.
Devices like the NTP time server often receive atomic clock signals form places such as NIST or NPL via long wave radio. Another method for receiving time from atomic clocks is using the GPS network (Global Positioning System).
The GPS network and satellite navigation are in fact a good example of why atomic clocks are needed with such high accuracy. Modern atomic clocks such as those found at NIST, NPL and inside orbiting GPS satellites are accurate to within a second every 100 million years or so. This accuracy is crucial when you examine how something like a cars GPS satellite navigation system works.
A GPS system works by triangulating the time signals sent from three or more separate GPS satellites and their onboard atomic clocks. Because these signals travel at the speed of light (nearly 100,000km a second) an inaccuracy of even one whole millisecond could put the navigational information out by 100 kilometres.
This high level of accuracy is also required for technologies such as air traffic control ensuring our crowded skies remain safe and is even critical for many Internet transactions such as trading in derivatives where the value can rise and fall every second.
| Richard N Williams is a technical author and specialist in atomic clocks, telecommunications, NTP and network time synchronisation helping to develop dedicated NTP clocks. Please visit us for more information about an NTP server or other NTP time server solutions. Article Source: http://EzineArticles.com/?expert=Richard_N_Williams |
The Atomic Clock and the Network Time Server
The atomic clock will be the culmination of mankind’s obsession of telling correct time. Before the atomic clock and also the nanosecond accuracy they, utilize time scales were based on the celestial bodies.
However, thank you for the development with the atomic clock it’s got now been realised that even the Earth in its rotation is not as accurate a measure of time because the atomic clock because it loses or gains a fraction of a second every single day.
Because of the want to possess a timescale primarily based fairly to the Earth’s rotation (astronomy and farming becoming two reasons) a timescale which is held by atomic clocks but adjusted for almost any slowing (or acceleration) in the Earth’s spin. This timescale is identified as UTC (Coordinated Universal Time) as employed across the globe making sure commerce and trade utilise the same time.
Computer networks use network time servers to synchronise to UTC time. Many folks refer to these time server gadgets as atomic clocks but which is inaccurate. Atomic clocks are extremely expensive and highly sensitive items of gear and are only normally to become found in universities or nationwide physics laboratories.
Fortunately nationwide physics laboratories like NIST (National Institute for Standards and Time – USA) and NPL (National Physical Laboratory – UK) broadcast the time signal from their atomic clocks. Alternatively the GPS network is another decent supply of correct time as each GPS satellite has onboard its very own atomic clock.
The network time server gets time from an atomic clock and distributes it utilizing a protocol for instance NTP (Network Time Protocol) making sure the computer network is synchronised for the identical time.
Because network time servers are managed by atomic clocks they are able to maintain incredibly accurate time; not losing a 2nd in hundreds if not thousands of years. This ensures the computer network is both safe and unsusceptible to timing problems as all devices may have the exact exact same time.
Find out more about network time.
http://ezinearticleshq.com/otherae/the-atomic-clock-and-the-network-time-server
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