A Penetration Depth Study on Li2Pd3B and Li2Pt3B

In this paper we present a penetration depth study on the newly discovered superconductors Li$_2$Pd$_3$B and Li$_2$Pt$_3$B. Surprisingly, the low-temperature penetration depth $f(T)$ demonstrates distinct behavior in these two isostructural compounds. In Li$_2$Pd$_3$B, $f(T)$ follows an exponential decay and can be nicely fitted by a two-gap BCS superconducting model with a small gap $\delta_1=3.2$K and a large gap $\delta_2=11.5$K. However, linear temperature dependence of $f(T)$ is observed in Li$_2$Pt$_3$B below 0.3$T_c$, giving evidence of line nodes in the energy gap.Comment: 2 pages, submitted to LT2

S-wave/spin-triplet order in superconductors without inversion symmetry: Li2_2Pd3_3B and Li2_2Pt3_3B

We investigate the order parameter of noncentrosymmetric superconductors Li$_2$Pd$_3$B and Li$_2$Pt$_3$B via the behavior of the penetration depth $\lambda(T)$. The low-temperature penetration depth shows BCS-like behavior in Li$_2$Pd$_3$B, while in Li$_2$Pt$_3$B it follows a linear temperature dependence. We propose that broken inversion symmetry and the accompanying antisymmetric spin-orbit coupling, which admix spin-singlet and spin-triplet pairing, are responsible for this behavior. The triplet contribution is weak in Li$_2$Pd$_3$B, leading to a wholly open but anisotropic gap. The significantly larger spin-orbit coupling in Li$_2$Pt$_3$B allows the spin-triplet component to be larger in Li$_2$Pt$_3$B, producing line nodes in the energy gap as evidenced by the linear temperature dependence of $\lambda(T)$. The experimental data are in quantitative agreement with theory.Comment: Phys. Rev. Lett. (in press). More details are include

Penetration depth study of LaOs4_4Sb12_{12}: Multiband s-wave superconductivity

We measured the magnetic penetration depth $\lambda(T)$ in single crystals of LaOs$_{4}$Sb$_{12}$ ($T_c$=0.74 K) down to 85 mK using a tunnel diode oscillator technique. The observed low-temperature exponential dependence indicates a s-wave gap. Fitting the low temperature data to BCS s-wave expression gives the zero temperature gap value $\Delta (0)= (1.34 \pm 0.07) k_B T_c$ which is significantly smaller than the BCS value of 1.76$k_B T_c$. In addition, the normalized superfluid density $\rho(T)$ shows an unusually long suppression near $T_c$, and are best fit by a two-band s-wave model.Comment: 5 pages, 2 figure

Demonstration of Bias-Controlled Algorithmic Tuning of Quantum Dots in a Well (DWELL) MidIR Detectors

The quantum-confined Stark effect in intersublevel transitions present in quantum-dots-in-a-well (DWELL) detectors gives rise to a midIR spectral response that is dependent upon the detector\u27s operational bias. The spectral responses resulting from different biases exhibit spectral shifts, albeit with significant spectral overlap. A postprocessing algorithm was developed by Sakoglu that exploited this bias-dependent spectral diversity to predict the continuous and arbitrary tunability of the DWELL detector within certain limits. This paper focuses on the experimental demonstration of the DWELL-based spectral tuning algorithm. It is shown experimentally that it is possible to reconstruct the spectral content of a target electronically without using any dispersive optical elements for tuning, thereby demonstrating a DWELL-based algorithmic spectrometer. The effects of dark current, detector temperature, and bias selection on the tuning capability are also investigated experimentally

Evolution of superconducting order in Pr(Os1−x_{1-x}Rux_{x})4_{4}Sb12_{12}

We report measurements of the magnetic penetration depth $\lambda$ in single crystals of Pr(Os$_{1-x}$Ru$_{x}$)$_{4}$Sb$_{12}$ down to 0.1 K. Both $\lambda$ and superfluid density $\rho_{s}$ exhibit an exponential behavior for the $x$$\geq$0.4 samples, going from weak ($x$=0.4,0.6), to moderate, coupling ($x$=0.8). For the $x$$\leq$0.2 samples, both $\lambda$ and $\rho_{s}$ vary as $T^{2}$ at low temperatures, but $\rho_{s}$ is s-wave-like at intermediate to high temperatures. Our data are consistent with a three-phase scenario, where a fully-gapped phase at $T_{c1}$ undergoes two transitions: first to an unconventional phase at $T_{c2}$$\lesssim$$T_{c1}$, then to a nodal low-$T$ phase at $T_{c3}$$<$$T_{c2}$, for small values of $x$.Comment: Changed title, enlarged numbering in figures 5 pages, 4 figures, 1 tabl

Temperature Conditions Existing in a Diffusion Type Cloud Chamber

There are many types of detectors of radioactive rays, such as Geiger Counters, ionization chambers, photographic emulsions, electroscopes, and cloud chambers. Many of these give only information such as the amount of radiation or the minimum energy of the rays because the information is registered as a change in voltage or a “count”. Outstanding among the different kinds of detectors is the type commonly called “cloud chambers”. In a cloud chamber the path of the ray* can actually be seen and photographed, its radius of curvature in an electric or magnetic field can be measured, the amount of ionization can be measured by counting the number of ions per length of path, and the amount of deviation from the predicted normal path can be studied. From this type of information the mass, velocity, and charge of the ray can be determined. The basic principle utilized in any chamber is that a gas which is supersaturated with a vapor will act as a means of detection of radioactive rays by forming a cloud trail along the path of the ray. The most common method of obtaining a gas which is supersaturated with a vapor is by cooling. Gas which has been saturated with vapor can be cooled until a high degree of supersaturation is reached if there are no particles in it to act as nuclei around which droplets can form. J.Aitken during his investigations (about 1880) indicated that dust particles do act as such nuclei and utilized the fact to count dust particles. In 1896 C.T.R. Wilson showed that ions formed in a supersaturated gas could also act as centers of condensation. This fact led Wilson to the discovery of his famous “expansion” cloud chamber. It is theorized that high energy rays in their motion through matter ionize many atoms along their path. These ions form nuclei for condensation, thus producing a trail of droplets which are visible to the eye and which also can be photographed if desired. The method used by Wilson for obtaining the supersaturated gas is expansion of a saturated gas by means of piston on the floor of the chamber. This sudden increase of volume causes a decrease of temperature, thus causing the gas to become supersaturated. The main disadvantage in Wilson’s chamber is that it will show tracks for only a very short period of time after expansion and then must be recycled for the next expansion. Therefore, there has been considerable interest in some kind of chamber that would be continuously sensitive. The first continuously sensitive cloud chamber was reported by L.G. Hoxton in 1933. This cloud chamber operated by passing air over water at 70C and thence into a water-jacketed observing channel at room temperature. Condensation phenomena were produced by electric discharges but not by radiation, so this method was not satisfactory. In 1936 R. E. Vollrath described a continuous cloud chamber that operated by interdiffusion of two vapors such as hydrochloric acid vapor and water vapor, at the interface of which the gas became supersaturated with respect to the mixture (dilute hydrochloric acid). A.Langsdorf, Jr. reported progress on a continuous diffusion cloud chamber in 1936. The construction of Langsdorf’s chamber is essentially a glass cylinder with a refrigerated floor and a heated roof. Through the roof the vapor of a liquid with a high vapor pressure is allowed to diffuse and saturate the gas in the chamber. Then as the saturated gas diffuses downward it becomes cooled and thus supersaturated and within a limited region acts as an ion detector. Although diffusion chambers have the advantage of being continuous, they frequently have the disadvantage of having diffuse, fuzzy, or distorted tracks which do not generally present a great problem in a well-designed Wilson expansion chamber. There is a definite need to find out more about the conditions that exist in diffusion chambers in order to improve their design. The purpose of this paper is to investigate some of the conditions that exist in a diffusion chamber, similar to the type proposed by Langsdorf

Probing the Processes of Planet Formation via Studies of the ϵ Chameleonitis Association

Nearby Young Moving Groups (NYMGs), i.e., loose groups of stars of age \u3c100 Myr in the solar vicinity, present ideal, accessible observational laboratories for studies on star and planet formation. Studying individual members of NYMGs, especially those hosting protoplanetary disks, in the infrared and millimeter regimes gives astronomers key information on disk evolution and the planet formation process. In this dissertation, I present an analysis of newly available data for members of one of the youngest known NYMGs, the Epsilon Chameleonitis Association (ECA), including detailed studies of two ECA members that host protoplanetary disks viewed at high inclinations (i.e. within ~30 degrees of edge-on). Through analysis of Gaia Space Astrometry Mission data for the ECA, I present updated constraints on the Galactic positions and kinematics and color-magnitude diagram positions of ECA members and candidates. I reassess their membership status and refine estimates of the multiplicity and disk fraction of the group. I determine a mean distance to ECA of 101.0±4.6 pc and confirm that, at an age of 5±3 Myr, it represents the youngest stellar group within ~100 pc of Earth. The two nearly edge-on star-disk systems studied here are representative of the diversity of planet-forming environments around young stars. The first, 2M1155-79B, was discovered during the aforementioned Gaia study of the ECA. Near-infrared spectra of 2M1155-79B, along with analysis of photometry from Gaia EDR3, 2MASS, VHS, and WISE, reveal that 2M1155-79B is most likely a young, late-M, star near the hydrogen-burning limit that is partially obscured by, and actively accreting from, a nearly edge-on circumstellar disk. The second planet-forming disk studied here orbits T Cha, a near solar-mass ECA member. I present archival Atacama Large Millimeter Array images of the millimeter continuum and 12CO (3-2) and 13CO (3-2) emission from the highly inclined (i~73°) T Cha disk. Radial brightness profiles show a limb-brightened ring of CO gas orbiting inside of the large dust grains generating the millimeter continuum, surrounded by a radially and vertically extended region of CO gas out to radii of ~200 AU that modelling reveals is likely probing the vertical freeze-out. These analyses illustrate the future potential of the ECA for providing new insights into star and planet formation processes

Assessing Internal Audit Quality

Internal audit quality is an issue of great importance to both the internal and external audit professions. PCAOB Auditing Standard No 2 highlights this importance when addressing the reliance that the external auditor can place on the internal audit work product. The study discussed here experimentally tests the influence of the source of the internal audit function on both the internal and external auditors\u27 evaluation of the quality of the internal audit function. To assess the importance of the internal audit function\u27s sourcing arrangement in the internal audit function\u27s quality assessment, the researchers employ a case study approach, modifying a case that has been used in prior research. The researchers find that for three of the four measured internal audit function quality characteristics, there was no difference in the assessment of the internal audit function between internal and external auditors, regardless of whether or not the internal audit function was provided in-house or was outsourced to a CPA firm other than the external auditor\u27s firm

An initial event in insect innate immune response: structural and biological studies of interactions between β-1,3-glucan and the N-terminal domain of β-1,3-glucan recognition protein

In response to invading microorganisms, insect β-1,3-glucan recognition protein (βGRP), a soluble receptor in the hemolymph, binds to the surfaces of bacteria and fungi and activates serine protease cascades that promote destruction of pathogens by means of melanization or expression of antimicrobial peptides. Here we report on the NMR solution structure of the N-terminal domain of βGRP (N-βGRP) from Indian meal moth (Plodia interpunctella), which is sufficient to activate the prophenoloxidase (proPO) pathway resulting in melanin formation. NMR and isothermal calorimetric titrations of N-βGRP with laminarihexaose, a glucose hexamer containing β-1,3 links, suggest a weak binding of the ligand. However, addition of laminarin, a glucose polysaccharide (~ 6 kDa) containing β-1,3 and β-1,6 links that activates the proPO pathway, to N-βGRP results in the loss of NMR cross-peaks from the backbone 15N-1H groups of the protein, suggesting the formation of a large complex. Analytical ultra centrifugation (AUC) studies of formation of N-βGRP:laminarin complex show that ligand-binding induces sel-fassociation of the protein:carbohydrate complex into a macro structure, likely containing six protein and three laminarin molecules (~ 102 kDa). The macro complex is quite stable, as it does not undergo dissociation upon dilution to sub-micromolar concentrations. The structural model thus derived from the present studies for N-βGRP:laminarin complex in solution differs from the one in which a single N-βGRP molecule has been proposed to bind to a triple helical form of laminarin on the basis of an X-ray crystallographic structure of N-βGRP:laminarihexaose complex [Kanagawa, M., Satoh, T., Ikeda, A., Adachi, Y., Ohno, N., and Yamaguchi, Y. (2011) J. Biol. Chem. 286, 29158-29165]. AUC studies and phenoloxidase activation measurements carried out with the designed mutants of N-βGRP indicate that electrostatic interactions involving Asp45, Arg54, and Asp68 between the ligand-bound protein molecules contribute in part to the stability of N-βGRP:laminarin macro complex and that a decreased stability is accompanied by a reduced activation of the proPO pathway. Increased β-1,6 branching in laminarin also results in destabilization of the macro complex. These novel findings suggest that ligand-induced self-association of βGRP:β-1,3-glucan complex may form a platform on a microbial surface for recruitment of downstream proteases, as a means of amplification of the initial signal of pathogen recognition for the activation of the proPO pathway

Proton–hydride tautomerism in hydrogen evolution catalysis

Efficient generation of hydrogen from renewable resources requires development of catalysts that avoid deep wells and high barriers. Information about the energy landscape for H_2 production can be obtained by chemical characterization of catalytic intermediates, but few have been observed to date. We have isolated and characterized a key intermediate in 2e^– + 2H^+ → H_2 catalysis. This intermediate, obtained by treatment of Cp*Rh(bpy) (Cp*, η^5-pentamethylcyclopentadienyl; bpy, κ^2-2,2′-bipyridyl) with acid, is not a hydride species but rather, bears [η^4-Cp*H] as a ligand. Delivery of a second proton to this species leads to evolution of H_2 and reformation of η^5-Cp* bound to rhodium(III). With suitable choices of acids and bases, the Cp*Rh(bpy) complex catalyzes facile and reversible interconversion of H^+ and H_2