Microfluidic and Nanofluidic Cavities for Quantum Fluids Experiments

The union of quantum fluids research with nanoscience is rich with opportunities for new physics. The relevant length scales in quantum fluids, 3He in particular, are comparable to those possible using microfluidic and nanofluidic devices. In this article, we will briefly review how the physics of quantum fluids depends strongly on confinement on the microscale and nanoscale. Then we present devices fabricated specifically for quantum fluids research, with cavity sizes ranging from 30 nm to 11 microns deep, and the characterization of these devices for low temperature quantum fluids experiments.Comment: 12 pages, 3 figures, Accepted to Journal of Low Temperature Physic

Government Expenditure, Foreign Direct Investment and Economic Growth in Nigeria

Government expenditure and Foreign Direct Investment (FDI) are vital macroeconomic variables of any economy as they are strong propellant of economic growth. The need to control and monitoring government spending and the FDI so as to achieve a steady economic growth necessitated this study. The study seeks to determine the impact of government expenditure and FDI on the Nigeria economic growth. A multiple regression analysis was used to test the relationship between government expenditure (capital and recurrent expenditure) and FDI as the explanatory variables on GDP (proxy for economic growth) as the dependent variable. Our result revealed that the explanatory variables: CEXP, REXP and FDI had significant relationship with economic growth. However CEXP did not conform to expectation. Some recommendations such as a thorough and accountable management of capital and recurrent expenditures in Nigeria, adequate planning, an effective macroeconomic framework and conducive economic environment to encourage foreign direct investment is require

High frequency sound in superfluid 3He-B

We present measurements of the absolute phase velocity of transverse and longitudinal sound in superfluid 3He-B at low temperature, extending from the imaginary squashing mode to near pair-breaking. Changes in the transverse phase velocity near pair-breaking have been explained in terms of an order parameter collective mode that arises from f-wave pairing interactions, the so-called J=4- mode. Using these measurements, we establish lower bounds on the energy gap in the B-phase. Measurement of attenuation of longitudinal sound at low temperature and energies far above the pair-breaking threshold, are in agreement with the lower bounds set on pair-breaking. Finally, we discuss our estimations for the strength of the f-wave pairing interactions and the Fermi liquid parameter, F4s.Comment: 15 pages, 8 figures, accepted to J. Low Temp. Phy

Imaginary Squashing Mode Spectroscopy of Helium Three B

We have made precision measurements of the frequency of a collective mode of the superfluid 3He-B order parameter, the J=2- imaginary squashing mode. Measurements were performed at multiple pressures using interference of transverse sound in an acoustic cavity. Transverse waves propagate in the vicinity of this order parameter mode owing to off-resonant coupling. At the crossing of the sound mode and the order parameter mode, the sound wave is strongly attenuated. We use both velocity and attenuation measurements to determine precise values of the mode frequency with a resolution between 0.1% and 0.25%.Comment: 6 pages, 4 figures, submitted to proceedings of Quantum Fluids and Solids (QFS) Conference 2006; revised 9/26/0

Anisotropic Aerogels for Studying Superfluid 3^3He

It may be possible to stabilize new superfluid phases of $^{3}$He with anisotropic silica aerogels. We discuss two methods that introduce anisotropy in the aerogel on length scales relevant to superfluid $^{3}$He. First, anisotropy can be induced with uniaxial strain. A second method generates anisotropy during the growth and drying stages. We have grown cylindrical $\sim$98% aerogels with anisotropy indicated by preferential radial shrinkage after supercritical drying and find that this shrinkage correlates with small angle x-ray scattering (SAXS). The growth-induced anisotropy was found to be $\sim90^\circ$ out of phase relative to that induced by strain. This has implications for the possible stabilization of superfluid phases with specific symmetry.Comment: 6 pages, 4 figures, submitted to Quantum Fluids and Solids (QFS) conference 200

Superconducting String Texture

We present a detailed analytical and numerical study of a novel type of static, superconducting, classically stable string texture in a renormalizable topologically trivial massive U(1) gauge model with one charged and one neutral scalar. An upper bound on the mass of the charged scalar as well as on the current that the string can carry are established. A preliminary unsuccesful search for stable solutions corresponding to large superconducting loops is also reported.Comment: RevTex, 14 pages, 8 figure

The Swiss Board Directors Network in 2009

We study the networks formed by the directors of the most important Swiss boards and the boards themselves for the year 2009. The networks are obtained by projection from the original bipartite graph. We highlight a number of important statistical features of those networks such as degree distribution, weight distribution, and several centrality measures as well as their interrelationships. While similar statistics were already known for other board systems, and are comparable here, we have extended the study with a careful investigation of director and board centrality, a k-core analysis, and a simulation of the speed of information propagation and its relationships with the topological aspects of the network such as clustering and link weight and betweenness. The overall picture that emerges is one in which the topological structure of the Swiss board and director networks has evolved in such a way that special actors and links between actors play a fundamental role in the flow of information among distant parts of the network. This is shown in particular by the centrality measures and by the simulation of a simple epidemic process on the directors network.Comment: Submitted to The European Physical Journal

Globally Anisotropic High Porosity Silica Aerogels

We discuss two methods by which high porosity silica aerogels can be engineered to exhibit global anisotropy. First, anisotropy can be introduced with axial strain. In addition, intrinsic anisotropy can result during growth and drying stages and, suitably controlled, it can be correlated with preferential radial shrinkage in cylindrical samples. We have performed small angle X-ray scattering (SAXS) to characterize these two types of anisotropy. We show that global anisotropy originating from either strain or shrinkage leads to optical birefringence and that optical cross-polarization studies are a useful characterization of the uniformity of the imposed global anisotropy.Comment: 18 pages, 14 figures, submitted to Journal of Non-Crystalline Solid

Long-Wavelength Instability in Surface-Tension-Driven Benard Convection

Laboratory studies reveal a deformational instability that leads to a drained region (dry spot) in an initially flat liquid layer (with a free upper surface) heated uniformly from below. This long-wavelength instability supplants hexagonal convection cells as the primary instability in viscous liquid layers that are sufficiently thin or are in microgravity. The instability occurs at a temperature gradient 34% smaller than predicted by linear stability theory. Numerical simulations show a drained region qualitatively similar to that seen in the experiment.Comment: 4 pages. The RevTeX file has a macro allowing various styles. The appropriate style is "mypprint" which is the defaul

Poly-instanton Inflation

We propose a new inflationary scenario in type IIB Calabi-Yau compactifications, where the inflaton is a K\"ahler modulus parameterising the volume of an internal four-cycle. The inflaton potential is generated via poly-instanton corrections to the superpotential which give rise to a naturally flat direction due to their double exponential suppression. Given that the volume mode is kept stable during inflation, all the inflaton-dependent higher dimensional operators are suppressed. Moreover, string loop effects can be shown to be negligible throughout all the inflationary dynamics for natural values of the underlying parameters. The model is characterised by a reheating temperature of the order $T_{\rm rh}\simeq 10^6$ GeV which requires $N_e \simeq 54$ e-foldings of inflation. All the inflationary observables are compatible with current observations since the spectral index is $n_s \simeq 0.96$, while the tensor-to-scalar ratio is $r\simeq 10^{-5}$. The volume of the Calabi-Yau is of order $10^3$ in string units, corresponding to an inflationary scale around $10^{15}$ GeVComment: 20 pages, 4 figure