The conceptual problems arise with momentum. The system’s total momentum increases as it begins to move. But where does this momentum come from? Shawyer had no convincing explanation, and critics said this was an obvious violation of the law of conservation of momentum.
McCulloch says there is observational evidence for this in the form of the famous fly by anomalies. These are the strange jumps in momentum observed in some spacecraft as they fly past Earth toward other planets. That’s exactly what his theory predicts.
The researchers used a cellulose material for the substrate of the chip, which is the part that supports the active semiconductor layer. Taken from cellulose, a naturally abundant substance used to make paper, cellulose nanofibril (CNF) is a flexible, transparent and sturdy material with suitable electrical properties.
Because these new magnets also have energy efficient characteristics, they can be used to create a new generation of sensors and actuators with vanishingly small heat signatures, said the researchers. These magnets could also find applications in efficient energy harvesting devices; compact micro-actuators for aerospace, automobile, biomedical, space and robotics applications; and ultra-low thermal signature actuators for sonars and defense applications.
Since these new magnets are composed of alloys that are free of rare-earth elements, they could replace existing rare-earth based magnetostriction alloys, which are expensive and feature inferior mechanical properties, said researchers.
You can see such symmetry breaking in a once-common 20th century technology: the two-wire ribbons used during television’s first few decades to send RF signals from rooftop VHF antennas to television sets without any loss. The electric RF current in the two conductors flow in opposite directions and have opposite phase. Because of the translational symmetry (the two conductors are parallel) the radiation fields cancel each other out, so there is no net radiation into space. But if you would flare the ends of the two conductors at one end of the ribbon, they aren’t parallel anymore and you break the translational symmetry. The two electric fields are no longer aligned and don’t cancel each other out, causing the RF signal to be converted into electromagnetic radiation.
Heat makes atoms move and can shake Cooper pairs apart, so the holy grail is to design a material where the pairs are bound together so strongly that superconductivity can happen even up to room temperature. It might be possible to describe a Fermi surface that would create that condition, and perhaps then imagine what crystal structure it would require. “Ideally we would like to be able to tell the materials scientist to put elements X, Y and Z together,” Lee said. “Unfortunately we can’t do that yet.”
To understand how current flows in a material you first have to understand electrons behave in a material. The key feature of solid state physics is that many materials are crystals. This means that the atoms are spaced periodically. As you mention, band structures are the way that we summarize the effect of this periodic potential. Basically, a band structure just relates an electrons momentum p=mv=hbar k to its energy. The momentum can be positive or negative, the sign only denotes direction. In free space this is very boring, Energy=m v2 /2 = p2 /2m=hbar k2 /2m. When you throw in a periodic potential, this becomes modified and results in bands. Actually calculating band structures is quite difficult. The key idea is that there are ranges of energy where the electron can live and ranges of energy where the electron cannot live.
Patch antennas focus the radio beam within a specific area. (A couple of vendors, Ruckus Wireless and Xirrus, have developed their own built-in “smart” antennas that adjust and focus Wi-Fi signals on clients.) Depending on the beamwidth, the effect can be that of a floodlight or a spotlight, says Jeff Lime, Ventev’s vice president. Ventev’s newest TerraWave High-Density products focus the radio beam within narrower ranges than some competing products, and offer higher gain (in effect putting more oomph into the signal to drive it further), he says.
At Georgia Tech, each antenna focused the Wi-Fi signal from a specific overhead access point to cover a section of seats below it. Fewer users associate with each access point. The result is a kind of virtuous circle. “It gives more capacity per user, so more bandwidth, so a better user experience,” says Lime.
I intend to examine the prospects of ultrasonics for wireless, local area communication. In other words, I will try to decide whether or not it might be feasable to create a system for objects in the same room to communicate with one another by sharing information through ultrasonic sound. To do this, I will work through issues such as the spectrum, transducers, beam width, transmission distance, bandwidth, and noise.
This work builds on the work done by Vadim Gerasimov, in the Things That Talk project, that transmits data by sound in the audible range. His site is a good starting point to visit before working through this information.