Heat transfer at low temperatures: Application to sapphire

It is found that at low temperatures, the Callaway expression for the lattice thermal conductivity of a sample having dislocations reduces to the expression obtained by Dubey based on the nonlinear heat transfer theory. The obtained expression is used to explain the measurements of Wolfimeyer and Dillinger of phonon conductivity of sapphire in the temperature range 0.4–4 K.     

Magnetic properties of corrosion products investigated by CEMS at low temperatures near 4.2 K

Conversion electron Mössbauer measurements with a proportional counter at 6.3, 78 and 300 K have been done to investigate the magnetic properties of the corrosion products formed on the surface of iron foils, which consist of small particles of γ-Fe₂O₃. The growing period of the corroded layer formed in a solution of low oxygen concentration has insignificant influence on the size of particles composing the layer, however, when the corroded layer is grown in a solution of comparatively high oxygen concentration, the particle size becomes large with growing period of the layer.     

Thermoelectric measurements on tungsten at ultra low temperatures

Measurements are reported of the thermoelectric ratio G for three zone-refined tungsten samples at temperatures down to 45 mK. For the purest sample $\text{(}\text{R}{}_{\mathrm{300K}}\text{R}{}_{\mathrm{0K}}\text{= 44 000)}$, G behaves simply and in accord with expectations. For two less pure samples $\text{(}\text{R}{}_{\mathrm{300K}}\text{R}{}_{\mathrm{0K}}\text{= 44 000 and 22 000)}$, G behaves anomalously, becoming increasingly more negative with decreasing temperature down to at least 45 mK. This anomalous behavior is tentatively attributed to trace amounts of iron.     

固体材料低温热导率的测量

本实验以4.2K二级G-M制冷机为冷源,采用稳态轴向热流法测量了304不锈钢与环氧玻璃钢在低温下的热导率,讨论了样品上初始温差的成因及其影响,给出了热导率真实值所在的区间,并对测量误差以及各种漏热带来的影响进行了分析。     

A low cost PC based card for heat-capacity measurements at low temperatures

We describe a simple, low cost pc based card for the measurement of heat capacity using adiabatic calorimetry at low temperatures. This card provides the control pulse to the sample heater as well as trigger pulse to the nano-voltmeter which monitors the sensor voltage (Ge sensor, Lake Shore Inc., USA). We have also added a 12 bit DAC on this card and this is used for remote setting of the heater current of an old SHE (now Biomagnetic, Inc., USA, model CCS) analog constant current source. Although this card is used here for heat-capacity measurements, the same can also be used for thermo-power and thermal-conductivity measurements.     

Mutual inductance bridge for magnetic relaxation measurements at low temperatures

An apparatus using a mutual inductance bridge has been designed to measure real and imaginary parts of the magnetic ac susceptibility simultaneously in the frequency range from 1 Hz to 230 kHz at helium temperatures. From 230 kHz up to 3 MHz the real part can be determined. The susceptibility as a function of temperature or external magnetic field at constant frequency may be measured. In addition, frequency sweeps can be performed with temperature and magnetic field held constant. The experiment is controlled by an on-line computer.     

Magnetization measurements of polycrystal ZnMn alloys at very low temperatures

The magnetization of ZnMn alloys with Mn concentration ranging from 68 to 1 ppm has been measured from 2 K down to 10 mK. The results show large departures from free spin behavior due to impurity-impurity interactions and some concentration independent effects.     

High resolution measurements of the ruby R1 line at low temperatures

A high resolution, resonance fluorescence technique is described which can overcome macroscopic strain broadening effects on the inhomogeneous lineshape of zero phonon lines. A linewidth of 1.21 GHz (fwhm) was observed for the ruby R₁ line at 15 K.     

Baryogenesis at low reheating temperatures

We note that the maximum temperature during reheating can be much greater than the reheating temperature T(r) at which the universe becomes radiation dominated. We show that the standard model anomalous (B+L)-violating processes can therefore be in thermal equilibrium for 1 GeV less, similarT(r)<100 GeV. Electroweak baryogenesis could work and the traditional upper bound on the Higgs mass coming from the requirement of the preservation of the baryon asymmetry may be relaxed. Alternatively, the baryon asymmetry may be reprocessed by sphaleron transitions either from a (B-L) asymmetry generated by the Affleck-Dine mechanism or from a chiral asymmetry between e(R) and e(L) in a B-L = 0 universe.     

The triple-alpha-reaction at low temperatures

We have studied the triple-α-reaction at low temperatures which is of importance on accreting white dwarfs and neutron stars. Although we have improved a recent investigation of Nomoto, Thielemann and Miyaji on several points, we find a reaction rate for the relevant temperature range (T=10⁷?10⁸K) which is rather similar to the previous result. In particular, our improved study confirms that helium might be ignited on accreting white dwarfs at temperaturesT≦4.10⁷ K.     

Light quarks at low temperatures

We show that for small quark masses, low temperatures and large volumes, the main features of the QCD partition function can be predicted on the basis of chiral symmetry. In particular, we establish a low-temperature theorem which governs the temperature dependence of the fermion condensate.     

Interaction of methanol with ZnO surfaces at low temperatures

Adsorption and condensation of methanol on polar (0001) faces of zinc oxide were studied by XPS and UPS. The results indicate that adsorbed CH₃OH is partly transformed to a precursor of a methoxy species at temperatures at low as 105 K. Adsorption saturates only at a coverage of about two monolayers. This double layer seems to become oriented by the structural influence of the (0001) face and stabilized by hydrogen bridge bonds. The sticking coefficient is of the order of 10^?2 while the condensation coefficient on top of the oriented double layer is as low as 10^?3. TDS on a polycrystalline ZnO film supports this model. No other species than CH₃OH occurred in desorption.     

Relaxation in glasses at low temperatures

JETP Letters - The interaction between tunneling system inherent in amorphous solids is established to be responsible for the universal behavior of their kinetics and thermodynamic properties at...     

Intensity measurements in the 2v3-band of 13CH4 at low temperatures

Absolute intensities of the J-multiplets P(1)-P(8), R(0)-R(7) and of the Q-branch in the 2v₃-band of ¹³CH₄ have been measured at 100, 150, 200, and 296°K. Our intensity data confirm the recent observation by Fox et al. that substitution of the isotope ¹³C for the central ¹²C atom in methane results in significantly different line strengths in the severely perturbed 2v₃-band. Our results at 296°K for the absolute intensities of R(0) and R(1) are in excellent agreement with the values measured by Fox et al.     

Quintessential inflation at low reheating temperatures

We have tested some simple quintessential inflation models, imposing the requirement that they match with the recent observational data provided by the BICEP and Planck team and leading to a reheating temperature, which is obtained via gravitational particle production after inflation, supporting the nucleosynthesis success. Moreover, for the models coming from supergravity one needs to demand low temperatures in order to avoid problems such as the gravitino overproduction or the gravitational production of moduli fields, which are obtained only when the reheating temperature is due to the production of massless particles with a coupling constant very close to its conformal value.     

High pressure techniques at low temperatures

Pramana - The article reviews the experimental techniques used in high pressure-low temperature investigations to study a variety of physico-chemical phenomena. The general principles of producing...     

Photoconductivity of semiconductors at low temperatures

Low-temperature oscillations in the photoconductivity of semiconductors are discussed. It is shown that oscillations will be observed if the probability for energy relaxation with optical phonons exceeds both the probability of carrier recombination and the energy-relaxation time for acoustic phonons. The oscillation shape is studied for momentum relaxation with acoustic phonons and with ionized impurities for the case in which interelectronic collisions can be neglected and when an account of these collisions leads to the establishment of an electron temperature.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 85–92, September, 1968.     

Cosmological baryon generation at low temperatures

Mechanisms for generating the net baryon number of the universe which do not involve grand unification are considered. Detailed calculations in a simple extension of the standard SU(3)×SU(2)×U(1) model are used to show that physics at temperatures of order 1 TeV can account for the observed baryon to entropy ratio. Some comments regarding alternatives to this simple model and some speculations concerning the implications for cosmology are offered.     

Transitions in glasses at low temperatures

Length-temperature measurements from ?180°C to the glass transition temperature have been made on a poly(vinyl alkyl ether) series, poly(ethylene terephthalate), and a tetrafluoroethylene-trifluoropropylene copolymer series.

Consistent with low frequency dynamic measurements, the poly(vinyl alkyl ethers) exhibit a glass-glass transition? Tgg [1] between Tg and Tg ?70°C with evidence of another at about ?160 to ?180°C. With increasing side-chain length, the expansion coefficient below Tg- and the magnitude of the g-g transition increase, and the value of the Simha-Boyer free-volume product decreases, suggesting retention of excess free volume by the flexible pendant group. This behavior is analogous to that observed for poly(alkyl methacrylates) except that the latter system exhibited two g-g transitions, the lower of which coincided with Tgg [1] observed here.

Poly(ethylene terephthalate) samples, both amorphous and crystalline, exhibit two T > Tg transitions at about ?85 and ?40°C. Dynamic results resolve only one relaxation in this temperature range.

The glass temperatures of the tetrafluoroethylene-trifluoropropylene copolymer series, as determined by both dilatometry and differential scanning calorimetry, extrapolate to a Tg, for 100% amorphous PTFE of 11-16°C. Two g-g transitions, present in each homo-polymer, persist in the copolymers, indicating that only a small number of molecular units are involved. The magnitude of these relaxations, however, as measured by the change in expansion coefficient, is dependent on copolymer composition.