Superconducting and normal state properties of ErRh4B4 and LuRh4B4

Detailed heat capacity measurements of the ternary compounds ErRh₄B₄ and LuRh₄B₄ have been performed between 0.5 and 36 K and in magnetic fields up to 4 kG, yielding new information on crystal field effects in these materials and on the influence of externally applied magnetic fields on the coupled superconducting-ferromagnetic reentrant transition in ErRh₄B₄. Static magnetic susceptibility data on LuRh₄B₄ are presented which allow qualitative conclusions to be drawn regarding the magnitude of exchange enhancement and orbital paramagnetic effects in the RERh₄B₄ compounds. The electrical resistivity of ErRh₄B₄ has also been determined between 4 K and room temperature.This research was supported by the Department of Energy under Contract Number Ey-76-S-03-0034-PA227-3 (LDW, HBM, RWM, MBM) and by the National Science Foundation under Grant Number NSF/DMR77-08469 (DCJ). One of us (RWM) thanks the National Science Foundation for a postdoctoral fellowship.     

Synaptic inputs mediating bipolar cell responses in the tiger salamander retina

Postsynaptic receptors in bipolar cells were studied by focal application of glutamate and GABA to the outer and inner plexiform layers (OPL and IPL) under visual guidance in living retinal slices of the tiger salamander. Two different types of conductance change could be elicited in bipolar cells by applying glutamate to the OPL. In off-center cells, which had axon telodendria ramifying in the distal 55% of the IPL, glutamate elicited a conductance increase associated with a reversal potential near -5 mV. In on-center cells, which had telodendria stratified in the proximal 45% of the IPL, glutamate caused a conductance decrease associated with a reversal potential near -11 mV. These observations suggest that glutamate gates relatively nonspecific cation channels at synapses between photoreceptors and bipolar cell dendrites. Application of glutamate to the IPL elicited no conductance change in Co2+ Ringer's solution, but in normal Ringer's it generated a conductance increase associated with a reversal potential near the chloride equilibrium potential (ECl). These findings are consistent with the notion that glutamate receptors exist in GABAergic and/or glycinergic amacrine cells, and that glutamate in the IPL depolarizes these cells, causing GABA and/or glycine release and the opening of chloride channels in bipolar cell axon terminals. In Co2+ Ringer's, application of GABA at the OPL elicited no conductance changes in bipolar cells, suggesting that GABA receptors do not exist on bipolar cell dendrites. Applied at the IPL, GABA elicited large conductance increases associated with a reversal potential near ECl. Implications of these results for the functional circuitry of the tiger salamander retina are discussed.     

Examining the relative effectiveness of different message framing strategies for child passenger safety: Recommendations for increased comprehension and compliance

Background

Age-appropriate child restraints and rear seating dramatically reduce injury in vehicle crashes. Yet parents and caregivers struggle to comply with child passenger safety (CPS) recommendations, and frequently make mistakes when choosing and installing restraints. The purpose of this research was to evaluate various methods of framing CPS recommendations, and to examine the relative effectiveness on parents’ knowledge, attitudes, and behavioral intentions related to best practices and proper use of child restraints. Emphasis framing is a persuasion technique that involves placing focus on specific aspects of the content in order to encourage or discourage certain interpretations of the content.

Method

A 5 (flyer group) X 2 (time) randomized experiment was conducted in which 300 parent participants answered a pre-survey, viewed one of four flyer versions or a no-education control version, and completed a post-survey. Surveys measured CPS knowledge, attitudes, perceptions of efficacy and risk, and behavioral intentions. The four flyers compared in this study all communicated the same CPS recommendations, but several versions were tested which each employed a different emphasis frame: (1) recommendations organized by the natural progression of seat types; (2) recommendations which focused on avoiding premature graduation; (3) recommendations which explained the risk-reduction rationale behind the information given; or (4) recommendations which were organized by age. In a fifth no-education (control) condition, participants viewed marketing materials.

Results

Analyses of covariance and pairwise comparisons indicated the risk-reduction rationale flyer outperformed other flyers for many subscales, and significantly differed from no-education control for the most subscales, including restraint selection, back seat knowledge, rear-facing knowledge and attitudes, total efficacy, overall attitudes, and stated intentions.

Conclusions

This research provides insight for increasing caregiver understanding and compliance with CPS information. Recommendations for the field include communicating the rationale behind the information given, using behavior-based directives in headers, avoiding age-based headers, and incorporating back-seat positioning directives throughout.     

Aging Effects in Gold Thermocompression Bonds to Complex Metallizations

The times to failure of Au thermocompression bonds to Au-Mo-Al and to Au-Ti-Al multilayer films were determined as a function of temperature over the range of 125-400°C and compared with the time to failure of gold bonds to aluminum films. A 500-? Ti intermediate film was found to be ineffective as a barrier to reaction between gold and aluminum. On the other hand, a 500-? Mo film was effective, providing increased time to failure over that observed for bonds to Au-Ti-Al and Al films. No failures were observed after 2000 hours at 400°C when gold wire bonds were made to an Au/Mo/Al metallization having 1000 ? of molybdenum as the intermediate layer.     

Transition from antiferromagnetism to ferromagnetism in the superconducting mixed ternary system (Sm1−x Er x )Rh4B4

The mixed ternary system (Sm_1–x Er _x )Rh₄B₄ has been investigated by means of measurements of ac electrical resistance in various applied magnetic fields, ac magnetic susceptibility, and specific heat. The low-temperature superconducting and magnetic transition temperature versus Er concentrationx phase diagram reveals the occurrence of a single transition to long-range magnetic order for all concentrations, changing from antiferromagnetism for SmRh₄B₄ to ferromagnetism for ErRh₄B₄ atx 0.2. The upper critical magnetic field versus temperature curves for various Er concentrations exhibit combined features characteristic of both SmRh₄B₄ and ErRh₄B₄, rather than a gradual evolution from one type to the other. A model for such a mixed magnetic system is discussed, and comparisons with other mixed ternary systems are made.Research supported by the U.S. Department of Energy under Contract No. DE-AT03-76ER70227.     

Intermediate valence behavior of ternary cerium and uranium transition metal borides

Low-temperature specific heat, electrical resistivity, ac magnetic susceptibility, and dc magnetization measurements were made on ternary cerium and uranium transition metal borides with the general formula CeT₃B₂ (T=Co, Ru, Rh, and Ir) and UT₃B₂ (T=Co, Ru, and Ir). The compound CeRu₃B₂ was found to exhibit superconductivity below 0.68 K. The values of the electronic specific heat coefficient range from 9.7 mJ/mole-K² for CeCo₃B₂ to 64 mJ/mole-K² for UIr₃B₂. The electrical resistivity versus temperature curves of all of the compounds exhibit negative curvature and are reminiscent of valence fluctuation behavior. In the case of CeIr₃B₂, the electrical resistivity attains a maximum value at 180 K, while the dc magnetic susceptibility has a temperature dependence that is typical of intermediate valence Ce compounds, approaching a finite value at zero temperature. The electrical resistivity of the ferromagnetic compound CeRh₃B₂ reveals a rapid decrease in spin disorder resistivity below 120 K. The dc magnetic susceptibility of this material can be described as the sum of a constant term and a Curie-Weiss contribution with an effective magnetic moment of 1.01 µ_B per formula unit and a Curie-Weiss temperature of 119 K. Magnetization measurements on CeRh₃B₂ yield a saturation magnetic moment of 0.37 µ_B per formula unit and a Curie temperature of 113 K.     

Non fermi liquid behavior in strongly correlated f-electron materials

Evidence for non Fermi liquid (NFL) behavior in y_1–x U_xPd₃ and related systems is reviewed and discussed within the context of possible microscopic mechanisms. Low temperature electrical resistivity, specific heat, and magnetic susceptibility measurements on the Th_1–xU_xPd₂Al₃ system reveal unconventional Kondo behavior with NFL low temperature characteristics. Magnetic susceptibility measurements on UCu_3.5Pd_1.5, which has previously been shown to exhibit NFL behavior, are presented. Some systematics of the NFL low temperature behavior observed in several f-electron materials include a linear temperature dependence of the electrical resistivity 1–aT with either positive or negative coefficient a, a logarithmically diverging specific heat C/T –lnT, and T^1/2 asymptotic behavior of the magnetic susceptibility 1 – T^1/2.     

Low-temperature properties of pseudoternary R(Rh1−x Ir x )4B4 (R=Ho and Dy) systems

Pseudoternary Ho(Rh_1–x Ir_x)₄B₄ and Dy(Rh_1–x Ir_x)₄B₄ systems were investigated with respect to the interplay between superconductivity (SC) and long-range magnetic ordering by means of specific heat (C) and upper critical magnetic field (H _c2) measurements. For Ho(Rh_1–x Ir_x)₄B₄ withx0.2 and Dy(Rh_1–x Ir_x)₄B₄ withx0.15, ferromagnetic (FM) ordering, reminiscent of spin-1/2 mean-field theory, was observed. In particular, FM ordering in Ho(Rh_1–x Ir_x)₄B₄ with 0.07x0.2 was found to destroy SC at a second critical temperatureT _c2 below the superconducting transition temperatureT _c, and was accompanied by a spike-shaped feature inC atT _c2. Coexistence of antiferromagnetic (AFM) ordering with SC was observed in both systems for 0.2x0.7. The compounds withx0.5 exhibited Néel temperaturesT _N that were smaller thanT _c and enhanced values ofH _c2 belowT _N. TheT _c andT _N undergo an abrupt decrease and increase, respectively, nearx0.5, and then cross atx0.6, above whichT _N>T _c. For Ho(Rh_1–x Ir_x)₄B₄ with 0.275x0.4, two different AFM transitions were detected in a double-peak feature inC.