Ca_3AlSb_3: an inexpensive, non-toxic thermoelectric material for waste heat recovery

Thermoelectric materials directly convert thermal energy into electrical energy, offering a promising solid-state solution for waste heat recovery. For thermoelectric devices to make a significant impact on energy and the environment the major impediments are the efficiency, availability and toxicity of current thermoelectric materials. Typically, efficient thermoelectric materials contain heavy elements such as lead and tellurium that are toxic and not earth abundant. Many materials with unusual structures containing abundant and benign elements are known, but remain unexplored for thermoelectric applications. In this paper we demonstrate, with the discovery of high thermoelectric efficiency in Ca_3AlSb_3, the use of elementary solid-state chemistry and physics to guide the search and optimization of such materials

Electrochemical Sensing with Metal Oxides

The effective sensing of hydrogen peroxide is important for a variety of reasons. It can be utilized as a diagnostic tool for diseases like asthma; also, the sensing can be utilized in pharmaceutical and food production for quality control. The use of silver oxide nanoparticles with varying morphologies has not been investigated as a sensing agent for hydrogen peroxide in the past. The particles’ properties and ability to oxidize and reduce hydrogen peroxide suggest that they will be effective to create a sensitive sensor. The silver oxide particles were prepared through chemical reduction using varying molar ratios of reactants. The varying ratios created three different particle shapes: hexapod, octahedral, and cubic. A three electrode system was to evaluate electrochemical properties, and the working electrode was coated with the silver oxide particles. Current response, detection limit, and electrical impedance spectroscopy (EIS) tests were done to gauge the effectiveness of the sensor, and X-ray diffraction (XRD), Zeta potential, and scanning electron microscopy (SEM) were performed to characterize the particles. The use of these particles has shown positive results for a sensor, with very high sensitivity and a good detection limit. The hexapods gave more response than the octahedral which gave more response than the cubic particles. The low stability suggests a new coating method must be investigated, but overall, the very high sensitivity of the silver oxide particles would be useful for aforementioned applications of hydrogen peroxide sensing

Medical Tourism Facilitators: Ethical Concerns about Roles and Responsibilities

Within the medical tourism industry are a number of key stakeholders – groups and individuals who champion the development of the industry, provide services within the industry, use the services of the industry, and/or are directly or indirectly impacted by the industry - who contribute to its expansion. One such group is facilitators, private agents who broker medical travel and foreign care arrangements between patients and destination facilities but are not employed by these facilities. Key to this element of the medical tourism industry is the Internet; facilitation companies in many countries have a strong web presence and rely primarily on websites (and secondarily on word-of-mouth) to advertise their services. Medical tourism brokers’ responsibilities toward medical tourists can include securing travel and accommodation needs, suggesting and booking facilities and surgeons abroad, contacting destination clinics, overseeing translation of medical records, arranging for tourist activities, and transferring medical records.These brokers can play an essential role in facilitating communication, providing information, and securing overall quality control by assessing the reputability and reliability of international facilities.It appears, however, that only a fraction of medical tourists actually use the services of brokers

Thermoelectric properties of the Yb_9Mn_(4.2-x)Zn_xSb_9 solid solutions

Yb_9Mn_(4.2)Sb_9 has been shown to have extremely low thermal conductivity and a high thermoelectric figure of merit attributed to its complex crystal structure and disordered interstitial sites. Motivated by previous work which shows that isoelectronic substitution of Mn by Zn leads to higher mobility by reducing spin disorder scattering, this study investigates the thermoelectric properties of the solid solution, Yb_9Mn_(4.2−x)Zn_xSb_9 (x = 0, 1, 2, 3 and 4.2). Measurements of the Hall mobility at high temperatures (up to 1000 K) show that the mobility can be increased by more than a factor of 3 by substituting Zn into Mn sites. This increase is explained by the reduction of the valence band effective mass with increasing Zn, leading to a slightly improved thermoelectric quality factor relative to Yb_9Mn_(4.2)Sb_9. However, increasing the Zn-content also increases the p-type carrier concentration, leading to metallic behavior with low Seebeck coefficients and high electrical conductivity. Varying the filling of the interstitial site in Yb_9Zn_(4+y)Sb_9 (y = 0.2, 0.3, 0.4 and 0.5) was attempted, but the carrier concentration (~10^(21) cm^(−3) at 300 K) and Seebeck coefficients remained constant, suggesting that the phase width of Yb_9Zn_(4+y)Sb_9 is quite narrow

Star Formation and AGN Activity in Galaxy Clusters from z=1−2z=1-2: a Multi-wavelength Analysis Featuring HerschelHerschel/PACS

We present a detailed, multi-wavelength study of star formation (SF) and AGN activity in 11 near-infrared (IR) selected, spectroscopically confirmed, massive ($\gtrsim10^{14}\,\rm{M_{\odot}}$) galaxy clusters at $1<z<1.75$. Using new, deep $Herschel$/PACS imaging, we characterize the optical to far-IR spectral energy distributions (SEDs) for IR-luminous cluster galaxies, finding that they can, on average, be well described by field galaxy templates. Identification and decomposition of AGN through SED fittings allows us to include the contribution to cluster SF from AGN host galaxies. We quantify the star-forming fraction, dust-obscured SF rates (SFRs), and specific-SFRs for cluster galaxies as a function of cluster-centric radius and redshift. In good agreement with previous studies, we find that SF in cluster galaxies at $z\gtrsim1.4$ is largely consistent with field galaxies at similar epochs, indicating an era before significant quenching in the cluster cores ($r<0.5\,$Mpc). This is followed by a transition to lower SF activity as environmental quenching dominates by $z\sim1$. Enhanced SFRs are found in lower mass ($10.1< \log \rm{M_{\star}}/\rm{M_{\odot}}<10.8$) cluster galaxies. We find significant variation in SF from cluster-to-cluster within our uniformly selected sample, indicating that caution should be taken when evaluating individual clusters. We examine AGN in clusters from $z=0.5-2$, finding an excess AGN fraction at $z\gtrsim1$, suggesting environmental triggering of AGN during this epoch. We argue that our results $-$ a transition from field-like to quenched SF, enhanced SF in lower mass galaxies in the cluster cores, and excess AGN $-$ are consistent with a co-evolution between SF and AGN in clusters and an increased merger rate in massive haloes at high redshift.Comment: 26 pages, 14 figures, 6 tables with appendix, accepted for publication in the Astrophysical Journa

Genome-Wide Occupancy of SREBP1 and Its Partners NFY and SP1 Reveals Novel Functional Roles and Combinatorial Regulation of Distinct Classes of Genes

The sterol regulatory element-binding protein (SREBP) family member SREBP1 is a critical transcriptional regulator of cholesterol and fatty acid metabolism and has been implicated in insulin resistance, diabetes, and other diet-related diseases. We globally identified the promoters occupied by SREBP1 and its binding partners NFY and SP1 in a human hepatocyte cell line using chromatin immunoprecipitation combined with genome tiling arrays (ChIP-chip). We find that SREBP1 occupies the promoters of 1,141 target genes involved in diverse biological pathways, including novel targets with roles in lipid metabolism and insulin signaling. We also identify a conserved SREBP1 DNA-binding motif in SREBP1 target promoters, and we demonstrate that many SREBP1 target genes are transcriptionally activated by treatment with insulin and glucose using gene expression microarrays. Finally, we show that SREBP1 cooperates extensively with NFY and SP1 throughout the genome and that unique combinations of these factors target distinct functional pathways. Our results provide insight into the regulatory circuitry in which SREBP1 and its network partners coordinate a complex transcriptional response in the liver with cues from the diet

High-Temperature Thermoelectric Properties of the Solid–Solution Zintl Phase Eu11Cd6Sb12–xAsx (x \u3c 3)

Zintl phases are compounds that have shown promise for thermoelectric applications. The title solid–solution Zintl compounds were prepared from the elements as single crystals using a tin flux for compositions x = 0, 1, 2, and 3. Eu11Cd6Sb12–xAsx (x \u3c 3) crystallize isostructurally in the centrosymmetric monoclinic space group C2/m (no. 12, Z = 2) as the Sr11Cd6Sb12 structure type (Pearson symbol mC58). Efforts to make the As compositions for x exceeding ∼3 resulted in structures other than the Sr11Cd6Sb12 structure type. Single-crystal X-ray diffraction indicates that As does not randomly substitute for Sb in the structure but is site specific for each composition. The amount of As determined by structural refinement was verified by electron microprobe analysis. Electronic structures and energies calculated for various model structures of Eu11Cd6Sb10As2 (x = 2) indicated that the preferred As substitution pattern involves a mixture of three of the six pnicogen sites in the asymmetric unit. In addition, As substitution at the Pn4 site opens an energy gap at the Fermi level, whereas substitution at the other five pnicogen sites remains semimetallic with a pseudo gap. Thermoelectric properties of these compounds were measured on hot-pressed, fully densified pellets. Samples show exceptionally low lattice thermal conductivities from room temperature to 775 K: 0.78–0.49 W/mK for x = 0; 0.72–0.53 W/mK for x = 1; and 0.70–0.56 W/mK for x = 2. Eu11Cd6Sb12 shows a high p-type Seebeck coefficient (from +118 to 153 μ V/K) but also high electrical resistivity (6.8 to 12.8 mΩ·cm). The value of zT reaches 0.23 at 774 K. The properties of Eu11Cd6Sb12–xAsx are interpreted in discussion with the As site substitution