Growth of single-crystal columns of CoSi2 embedded in epitaxial Si on Si(111) by molecular beam epitaxy

The codeposition of Si and Co on a heated Si(111) substrate is found to result in epitaxial columns of CoSi2 if the Si:Co ratio is greater than approximately 3:1. These columns are surrounded by a Si matrix which shows bulk-like crystalline quality based on transmission electron microscopy and ion channeling. This phenomenon has been studied as functions of substrate temperature and Si:Co ratio. Samples with columns ranging in average diameter from approximately 25 to 130 nm have been produced

Facilitation of polymer looping and giant polymer diffusivity in crowded solutions of active particles

We study the dynamics of polymer chains in a bath of self-propelled particles (SPP) by extensive Langevin dynamics simulations in a two dimensional system. Specifically, we analyse the polymer looping properties versus the SPP activity and investigate how the presence of the active particles alters the chain conformational statistics. We find that SPPs tend to extend flexible polymer chains while they rather compactify stiffer semiflexible polymers, in agreement with previous results. Here we show that larger activities of SPPs yield a higher effective temperature of the bath and thus facilitate looping kinetics of a passive polymer chain. We explicitly compute the looping probability and looping time in a wide range of the model parameters. We also analyse the motion of a monomeric tracer particle and the polymer's centre of mass in the presence of the active particles in terms of the time averaged mean squared displacement, revealing a giant diffusivity enhancement for the polymer chain via SPP pooling. Our results are applicable to rationalising the dimensions and looping kinetics of biopolymers at constantly fluctuating and often actively driven conditions inside biological cells or suspensions of active colloidal particles or bacteria cells.Comment: 15 pages, 9 figures, IOPLaTe

Synchronization and fault-masking in redundant real-time systems

A real time computer may fail because of massive component failures or not responding quickly enough to satisfy real time requirements. An increase in redundancy - a conventional means of improving reliability - can improve the former but can - in some cases - degrade the latter considerably due to the overhead associated with redundancy management, namely the time delay resulting from synchronization and voting/interactive consistency techniques. The implications of synchronization and voting/interactive consistency algorithms in N-modular clusters on reliability are considered. All these studies were carried out in the context of real time applications. As a demonstrative example, we have analyzed results from experiments conducted at the NASA Airlab on the Software Implemented Fault Tolerance (SIFT) computer. This analysis has indeed indicated that in most real time applications, it is better to employ hardware synchronization instead of software synchronization and not allow reconfiguration

Tomographic RF Spectroscopy of a Trapped Fermi Gas at Unitarity

We present spatially resolved radio-frequency spectroscopy of a trapped Fermi gas with resonant interactions and observe a spectral gap at low temperatures. The spatial distribution of the spectral response of the trapped gas is obtained using in situ phase-contrast imaging and 3D image reconstruction. At the lowest temperature, the homogeneous rf spectrum shows an asymmetric excitation line shape with a peak at 0.48(4)$\epsilon_F$ with respect to the free atomic line, where $\epsilon_F$ is the local Fermi energy

Thermalization of quark-gluon matter by 2-to-2 and 3-to-3 elastic scatterings

Thermalization of quark-gluon matter is studied with a transport equation that includes contributions of 2-to-2 and 3-to-3 elastic scatterings. Thermalization time is related to the squared amplitudes for the elastic scatterings that are calculated in perturbative QCD.Comment: LaTex, 6 pages, 3 figures, talk presented at the 19th international conference on ultra-relativistic nucleus-nucleus collisions, Shanghai, China, Nov. 200

Observation of Phase Separation in a Strongly-Interacting Imbalanced Fermi Gas

We have observed phase separation between the superfluid and the normal component in a strongly interacting Fermi gas with imbalanced spin populations. The in situ distribution of the density difference between two trapped spin components is obtained using phase-contrast imaging and 3D image reconstruction. A shell structure is clearly identified where the superfluid region of equal densities is surrounded by a normal gas of unequal densities. The phase transition induces a dramatic change in the density profiles as excess fermions are expelled from the superfluid.Comment: 5 pages, 7 figure

Thermally induced instability of a doubly quantized vortex in a Bose-Einstein condensate

We study the instability of a doubly quantized vortex topologically imprinted on $^{23}$Na condensate, as reported in recent experiment [Phys. Rev. Lett. \textbf{93}, 160406 (2004)]. We have performed numerical simulations using three-dimensional Gross-Pitaevskii equation with classical thermal noise. Splitting of a doubly quantized vortex turns out to be a process that is very sensitive to the presence of thermal atoms. We observe that even ve ry small thermal fluctuations, corresponding to 10 to 15% of thermal atoms, ca use the decay of doubly quantized vortex into two singly quantized vortices in tens of milliseconds. As in the experiment, the lifetime of doubly quantized vortex i s a monotonic function of the interaction strength.Comment: 4 pages, 5 figure

Influence Functionals and the Accelerating Detector

The influence functional is derived for a massive scalar field in the ground state, coupled to a uniformly accelerating DeWitt monopole detector in $D+1$ dimensional Minkowski space. This confirms the local nature of the Unruh effect, and provides an exact solution to the problem of the accelerating detector without invoking a non-standard quantization. A directional detector is presented which is efficiently decohered by the scalar field vacuum, and which illustrates an important difference between the quantum mechanics of inertial and non-inertial frames. From the results of these calculations, some comments are made regarding the possibility of establishing a quantum equivalence principle, so that the Hawking effect might be derived from the Unruh effect.Comment: 32 page

Avatars:the other side of Proteus's mirror : a study into avatar choice regarding perception

The trend for online interactions, can be regarded as being ‘anti-so-cially social’, meaning that a great deal of time is spent playing, working and socializing with the internet serving as the communication conduit. Within that Virtual Social Environment very deep relationships are formed and maintained without the parties ever having met each other face-to-face. Raising the question how much does the physical appearance of an avatar influence the perception of the person behind it? Are relationships informed by appearance even in the vir-tual world and what implications does that have for second language acquisition? This paper leads to a small-scale research project where a selection of avatars with various racially identifiable characteristics were used to identify which av-atars a second language speaker would feel more at ease interacting with in the target language. The resultant research aims to test three hypotheses regarding preferred avatar choice for second language users based solely on perceptions