Science

The leap second on June 30 will keep atomic clocks in synch with everyday timekeeping

If you’re one of those people who just can’t find the time to fit everything you want to do into a day, then mark June 30 on your calendar. On that Tuesday you’ll have a little extra time on your hands because, at precisely 23:59:59 GMT, the world’s clocks will add a second to the day, making it 24 hours and one second long.

Although a standard year is 365 days long, the Earth actually makes its journey around the Sun in about 365.25 days. This means that, over time, the calendar will start to get out of synch with the Sun, and the Vernal Equinox marking the beginning of spring will get later and later in the year. In fact, by 1586, the old Julian calendar invented by the Romans was off by a full 11 days.

To prevent this, the modern Gregorian calendar includes leap years. Most of us are familiar with the formula of adding an additional day every four years, but it’s actually a bit more complicated, stating that if a year is divisible by four, but is not divisible by 100, and is not divisible by 400, then it is a leap year. And even this is an approximation, but a necessary one if the seasons are to keep matching the calendar dates.

The leap second is based on a similar, but much more subtle and complex problem, which is how to reconcile the length of the day with the length of the second. At first this seems like the definition of a non-problem because a second is defined as 1/86,400th of a day. This means that whatever the length of the day is the second should, by definition, match.

The problem is that the Earth’s day has a maddeningly inconsistent length. The Earth is constantly being pulled at by the Moon, the Sun, and the planets, creating the tides that slowly, but surely slow down the Earth’s rotation. Worse, the Earth isn’t solid. Much of it is in a molten liquid or plastic state. To see how this affects the day, try spinning a hard-boiled egg and a raw one (in the shell, of course). The hard-boiled one will spin like a top while the raw one will fall over because the liquid yolk and white are sloshing about. A similar thing happens to the Earth, causing all sorts of unpredictable wobbles.

Added to this is the fact that the Earth’s crust isn’t stable either. Continents move, ice caps grow and shrink, as do glaciers, while land masses are pressed down and rebound as ice ages come and go and sea levels change. And when you add in volcanoes and earthquakes, it’s a wonder that the day is as steady as it is. However, it does change when measured astronomically against quasars and GPS measurements, and, according to NASA, the day has lengthened by an average of 2.5 milliseconds since 1820.

This variation doesn’t mean much in everyday life and it may seem like most people could live with a day that’s off by a couple of thousandths of a second, but we live in a world that requires extremely precise timing in order to function. Navigation, astronomy, mobile phones, satellites, the internet, submarines, and a huge number of other systems rely on extremely precise clocks – in this case, atomic clocks.

Thanks to atomic clocks, we now have two definitions of the second. The first is the imprecise one based on the rotation of the Earth, and the other, the official one used by the scientific community since the General Conference of the Metre Convention of 1967, is based on oscillations of a cesium atom with a second defined as 9,192,631,770 oscillations of the atom’s microwave signal.

This is where the leap second comes in. It’s based on the specifications of the International Earth Rotation and Reference Systems Service (IERS) in Paris and uses 200 atomic clocks in 50 national laboratories to keep the world’s radio and internet controlled timepieces within 0.9 seconds of accuracy over the course of a year.

The tricky bit is taking the extreme accuracy of the atomic clocks and matching them to the more variable rotation of the Earth, which by 1972 was already 10 seconds out of synch. To remedy this discrepancy, the atomic clocks are used to keep tabs on the Earth’s rotation. When astronomical measurements indicate that they clocks and the Earth are getting too far out of step, a correction is calculated and periodically applied, producing what is now called Coordinated Universal Time (UTC).

Since January 1, 1972, there have been 26 leap seconds. These leap seconds aren’t anything as regular as leap years. Instead of regular intervals, leap seconds have since 1999 been set at intervals of 7, 3, 3.5, and 3 years. During these leap seconds, clocks and watches showing legal time must synch with a new time signal or stop for one second.

Though the leap second is an established standard, its use remains controversial in horological circles due to the expense of keeping the two time systems in synch, and a decision on whether to continue the practice is expected to be made in November by the World Radiocommunication Conference (WRC-15) of the International Telecom Union Unia Transportation.

References:http://www.gizmag.com/

A few months ago, we reported on the development of a material that uses the same technique employed by gecko feet to allow its adhesion to be turned on and off at will. This allows fragile components, like those used in the manufacture of semiconductors, to be carefully picked up and put down without suction or residue-leaving adhesives. Now researchers at the University of Pennsylvania (UPenn) have developed a gripper, also inspired by the gecko and also tunable, that they claim is much simpler, making it easy and cheap to mass produce.

The material developed by scientists at Germany’s Leibniz Institute for New Materials (INM) that we looked at in March mimics the microscopic mushroom-shaped, hair-like projections known as setae that are found on gecko feet. So, just like gecko feet, the manmade microscopic pillars created by the INM team temporarily bond to surfaces at the molecular level thanks to the van der Waals force. To switch the stickiness off, the structure of the pillars is altered electronically. The problem is that making these complicated structures is, well, complicated.

“Other researchers have mimicked [gecko setae] structures to achieve tunable adhesion, but they are tough to make,” says UPenn graduate student Helen Minsky. “You can make a few of these structures, but, if you want to make larger arrays of them, it becomes much tougher. The angles and the flared tip means you can’t just slip them out of a mold.”

So although they also took inspiration from the gecko, Minsky and Kevin Turner, the Gabel Family Term Associate Professor in the School of Engineering and Applied Science’s Department of Mechanical Engineering and Applied Mechanics, have taken a different approach.

They created a simple cylindrical post structure that consists of a hard plastic core surrounded by a softer silicone rubber shell. While the structure doesn’t mimic the mushroom shape of the gecko’s setae, it achieves the same result through the soft rubber conforming to the surface and the stress from lifting being concentrated on the stiff inner core. The adhesion is switched off through the application of lateral force, which shifts the stress to the edges and allows a crack to form and the bond to break.

“When it comes to tunable adhesion, everyone is familiar with the gecko, and everyone tries to copy it,” says Turner. “The problem is that it’s really hard to manufacture complex structures as well as nature. We’ve come up with a strategy that can achieve similar adhesion behavior but is much easier to make.”

The researchers have created prototype grippers that are a few millimetres in diameter and are designed to grip smooth surfaces, such as glass. However, they claim their experiments and simulations indicate that the composite structure will work in the same way when scaled down to microscopic sizes.

References:http://www.gizmag.com/

Taking advantage of the unique light absorbing properties of plasmonic metatamaterials, researchers have printed color images using nanoscale holes instead of ink.

Using nanometer-size metamaterials, researchers at Missouri University of Science and Technology have developed a technique to print images that uses the manipulation of light, rather than the application of ink, to produce colors. This “no-ink” printing method has been demonstrated by producing a Missouri S&T athletic logo just 50 micrometers wide.

In normal color printing, various semi-transparent inks are applied on top of each other to produce the various hues of a picture. In the technique developed by Missouri S&T, instead of ink, microminiature perforations are made in a multi-layered structure consisting of two thin films of silver separated by a film of silica 45 nanometers thick. The uppermost layer of silver film, just 25 nanometers deep, is punctured with miniscule holes using a focused ion-beam milling microfabrication process.

Using this process, the researchers created holes with different diameters (ranging in size from 45 to 75 nanometers) corresponding to the desired absorption of light at various wavelengths. As such, light shining onto the logo at specific frequencies allowed researchers to create different colors with reflected light instead of ink. This nano-scale “color palette” meant that the physical characteristics of the holes in the material determined the color displayed to accurately reproduce the S&T athletic logo.

“Unlike the printing process of an inkjet or laserjet printer, where mixed color pigments are used, there is no color ink used in our structural printing process – only different hole sizes on a thin metallic layer,” said Dr. Jie Gao, assistant professor of mechanical and aerospace engineering at Missouri S&T.

The nanoscale perforations used to provide this color are so small as to only be visible with the help of an electron microscope, but they allowed the researchers to reproduce the standard colors of the S&T logo, and also to manipulate the light to produce four new colors to make an orange ampersand, a navy blue “Missouri”, a magenta “S” and “T”, and a cyan pickaxe symbol.

As the sandwiched silver/silica material acts as a plasmonic device, the Missouri S&T team believes that mechanical color printing on such materials provides a much higher printing resolution than conventional color printing. This is because their research shows that the periodic holes on the surface of the silver film provides excitation of surface-plasmon polaritons (electromagnetic waves that travel along the surface of a metal-dielectric or metal-air interface) and create an optical magnetic dipole resonance which results in near-perfect light absorption and negligible reflection in the material.

As a combination of substances that provide functions or phenomena that act in ways not yet found in nature, the printing substrate is also a metamaterial. As such, its unique properties may allow it to be used in ways not previously possible in the areas of nanoscale visual arts, security tagging, and information storage. The researchers also believe that such a method of printing should also result in a reduced material count in relation to standard printing methods, and could lead to lower costs, easier recycling, and higher fidelity and stability in image reproduction.

References:

A molecule found in avocado has shown promise as a potential drug to treat a form of leukemia

Acute myeloid leukemia (AML) is a type of cancer where blood stem cells evolve into abnormal blood cells, rather than the healthy cells the body would normally produce. These then build up in the bone marrow and crowd out the healthy cells, leading to infection and often death.

Professor Paul Spagnuolo from Canada’s University of Waterloo believes that the disease can be best combated at its core. He managed to identify a compound in avocado, called Avocatin B, which is precise in its targeting of the leukemia stem cells, and can be applied without causing peripheral damage to the surrounding cells.

“The stem cell is really the cell that drives the disease,” says Spagnuolo. “The stem cell is largely responsible for the disease developing and it’s the reason why so many patients with leukemia relapse. We’ve performed many rounds of testing to determine how this new drug works at a molecular level and confirmed that it targets stem cells selectively, leaving healthy cells unharmed.”

Spagnuolo’s work is still in its very early stages and he estimates Avocatin B-inspired leukemia medication to be years away from approval for human use. But he says it could one day greatly improve the quality of life and life expectancy for those suffering from AML. At present he is carrying out experiments with a view to preparing a drug for Phase I clinical trials.

References:http://www.gizmag.com/