Variable-transparency wall regulates temperatures of structures

An effective temperature regulating wall consists of one layer /e.g., one of the paraffins/ relatively opaque to thermal radiation in the solid state and transparent to it in the molten state and placed between two transparent layers. A mirror coating is applied to back layer

Gauge factor of thick film resistors: outcomes of the variable range hopping model

Despite a large amount of data and numerous theoretical proposals, the microscopic mechanism of transport in thick film resistors remains unclear. However, recent low temperature measurements point toward a possible variable range hopping mechanism of transport. Here we examine how such a mechanism affects the gauge factor of thick film resistors. We find that at sufficiently low temperatures $T$, for which the resistivity follows the Mott's law $R(T)\sim \exp(T_0/T)^{1/4}$, the gauge factor GF is proportional to $(T_0/T)^{1/4}$. Moreover, the inclusion of Coulomb gap effects leads to ${\rm GF}\sim (T_0'/T)^{1/2}$ at lower temperatures. In addition, we study a simple model which generalizes the variable range hopping mechanism by taking into account the finite mean inter-grain spacing. Our results suggest a possible experimental verification of the validity of the variable range hopping in thick film resistors.Comment: 7 pages, 3 eps figures, submitted to Journal of Applied Physic

Electron Transport in Disordered Graphene Nanoribbons

We report an electron transport study of lithographically fabricated graphene nanoribbons of various widths and lengths at different temperatures. At the charge neutrality point, a length-independent transport gap forms whose size is inversely proportional to the width. In this gap, electron is localized, and charge transport exhibits a transition between simple thermally activated behavior at higher temperatures and a variable range hopping at lower temperatures. By varying the geometric capacitance through the addition of top gates, we find that charging effects constitute a significant portion of the activation energy.Comment: 4 pages, 4 figure

A simple, ultrahigh vacuum compatible scanning tunneling microscope for use at variable temperatures

We present the construction of a very compact scanning tunneling microscope (STM) which can be operated at temperatures between 4 and 350 K. The tip and a tiny tip holder are the only movable parts, whereas the sample and the piezoscanner are rigidly attached to the body of the STM. This leads to an excellent mechanical stability. The coarse approach system relies on the slip-stick principle and is operated by the same piezotube which is used for scanning. As an example of the performance of the device, images of a NbSe2 surface with atomic resolution are obtained

Numerical Computation of Finite Size Scaling Functions: An Alternative Approach to Finite Size Scaling

Using single cluster flip Monte Carlo simulations we accurately determine new finite size scaling functions which are expressed only in terms the variable $x = \xi_L / L$, where $\xi_L$ is the correlation length in a finite system of size $L$. Data for the d=2 and d=3 Ising models, taken at different temperatures and for different size lattices, show excellent data collapse over the entire range of scaling variable for susceptibility and correlation length. From these finite size scaling functions we can estimate critical temperatures and exponents with rather high accuracy even though data are not obtained extremely close to the critical point. The bulk values of the renormalized four-point coupling constant are accurately measured and show strong evidence for hyperscaling.Comment: RevTex. 19 page

Anisotropic magnetization and resistivity of single crystalline RNi1-xBi2+-y (R = La-Nd, Sm, Gd-Dy)

We present a detailed study of RNi1-xBi2+-y (R = La-Nd, Sm, Gd-Dy) single crystals by measurements of stoichiometry and temperature dependent magnetic susceptibility, magnetization, and electrical resistivity. This series forms with partial Ni occupancy as well as a variable Bi occupancy. For R = Ce-Nd, Sm, Gd-Dy, the RNi1-xBi2+-y compounds show local-moment like behavior and order antiferromagnetically at low temperatures. Determination of anisotropies as well as antiferromagnetic ordering temperatures for RNi1-xBi2+-y (R = Ce-Nd, Sm, Gd-Dy) have been made. Although crystalline samples from this family exhibit minority, second phase superconductivity at low temperatures associated with Ni-Bi and Bi contamination, no evidence of bulk superconductivity has been observed

Dust Temperatures in the Infrared Space Observatory Atlas of Bright Spiral Galaxies

We examine far-infrared and submillimeter spectral energy distributions for galaxies in the Infrared Space Observatory Atlas of Bright Spiral Galaxies. For the 71 galaxies where we had complete 60-180 micron data, we fit blackbodies with lambda^-1 emissivities and average temperatures of 31 K or lambda^-2 emissivities and average temperatures of 22 K. Except for high temperatures determined in some early-type galaxies, the temperatures show no dependence on any galaxy characteristic. For the 60-850 micron range in eight galaxies, we fit blackbodies with lambda^-1, lambda-2, and lambda^-beta (with beta variable) emissivities to the data. The best results were with the lambda^-beta emissivities, where the temperatures were ~30 K and the emissivity coefficient beta ranged from 0.9 to 1.9. These results produced gas to dust ratios that ranged from 150 to 580, which were consistent with the ratio for the Milky Way and which exhibited relatively little dispersion compared to fits with fixed emissivities.Comment: AJ, 2003, in pres

Thermistor connector assembly increases accuracy of measurements

Isolation of the thermistor from spurious heat transfer for accurately measuring ambient air temperatures is accomplished by a mounting consisting of a transparent plastic film bonded to a U-shaped phenolic board with depositions of aluminum on each face and upper edge, and a variable capacitor for fine tuning