Scanning tunneling microscopy studies of fivefold surfaces of icosahedral Al-Pd-Mn quasicrystals and of thin silver films on those surfaces

Quasicrystals are non-periodic but well-ordered solids. Their unusual atomic structures foster peculiar surface properties such as low friction and enhanced oxidation resistance. This is well established at least for aluminum-rich icosahedral (i) quasicrystals. It is also very well known that sputter-annealed surfaces of i-Al-Pd-Mn possess step-terrace morphology even though a network of Bergman and Mackay clusters defines its bulk structure.;Using scanning tunneling microscope (STM) we have investigated clean fivefold surfaces of i-Al-Pd-Mn quasicrystals. In addition, we have examined the bulk structural models of icosahedral Al-Pd-Mn quasicrystals in terms of the densities, compositions and interplanar spacings for the fivefold planes. We focus on four models that contain no partial or mixed occupancies, but we have made some comparisons to a fifth model containing such sites. Each of the four models contains paired planes (layers) that can be separated into two main families on the basis of three features: the relative densities of the two planes, the gap separating the layer from the nearest atomic plane, and the Pd content in the topmost plane. We have compared these families with the available experimental data obtained for the fivefold surfaces. The experimental data and other arguments lead to the conclusion that the family with no Pd in the top plane is favored.;We have studied the nucleation and growth of Ag islands on the fivefold surface of the i-Al-Pd-Mn quasicrystal using STM. From 127 K to 300 K, the density of Ag islands remains constant but it drops as temperature increases beyond 300 K. To understand this behavior, we have developed a mean field rate equation model that takes into account the enhanced nucleation at traps relative to nucleation at regular terrace sites. The best fit to the model suggests that the critical sizes for the nucleation at both sites are large, especially at the traps, where six Ag atoms form stable clusters, and that binding between Ag atoms at the traps is stronger than at the regular terrace sites. In addition, we have identified these trap sites as the cut clusters in the aforementioned structure analysis

Formation of a Novel Ordered Ni3Al Surface Structure by Codeposition on NiAl(110)

The formation of a new type of ordered 2D Ni3Al overlayer by low-temperature codeposition on NiAl(110) is demonstrated by kinetic Monte Carlo simulation of a multisite atomistic lattice-gas model with a precise treatment of surface diffusion kinetics. Simultaneous codeposition with 3 1 Ni Al yields poor ordering at 300 K but well-ordered structures by ~500K. Sequential codeposition of Ni then Al yields unmixed core-ring nanostructures at 300 K but strong intermixing and ordering by ~500K

Identification of two Amino Acids in the C-terminal Domain of Mouse CRY2 Essential for PER2 Interaction

<p>Abstract</p> <p>Background</p> <p>Cryptochromes (CRYs) are a class of flavoprotein blue-light signaling receptors found in plants and animals, and they control plant development and the entrainment of circadian rhythms. They also act as integral parts of the central circadian oscillator in humans and other animals. In mammals, the CLOCK-BMAL1 heterodimer activates transcription of the <it>Per </it>and <it>Cry </it>genes as well as clock-regulated genes. The PER2 proteins interact with CRY and CKIε, and the resulting ternary complexes translocate into the nucleus, where they negatively regulate the transcription of <it>Per </it>and <it>Cry </it>core clock genes and other clock-regulated output genes. Recent studies have indicated that the extended C-termini of the mammalian CRYs, as compared to photolyase proteins, interact with PER proteins.</p> <p>Results</p> <p>We identified a region on mCRY2 (between residues 493 and 512) responsible for direct physical interaction with mPER2 by mammalian two-hybrid and co-immunoprecipitation assays. Moreover, using oligonucleotide-based degenerate PCR, we discovered that mutation of Arg-501 and Lys-503 of mCRY2 within this C-terminal region totally abolishes interaction with PER2.</p> <p>Conclusions</p> <p>Our results identify mCRY2 amino acid residues that interact with the mPER2 binding region and suggest the potential for rational drug design to inhibit CRYs for specific therapeutic approaches.</p

Arthrobots

This paper describes a class of robots—“arthrobots”— inspired, in part, by the musculoskeletal system of arthropods (spiders and insects, inter alia). An exoskeleton, constructed from thin organic polymeric tubes, provides lightweight structural support. Pneumatic joints modeled after the hydrostatic joints of spiders provide actuation and inherent mechanical compliance to external forces. An inflatable elastomeric tube (a “balloon”) enables active extension of a limb; an opposing elastic tendon enables passive retraction. A variety of robots constructed from these structural elements demonstrate i) crawling with one or two limbs, ii) walking with four or six limbs (including an insect-like triangular gait), iii) walking with eight limbs, or iv) floating and rowing on the surface of water. Arthrobots are simple to fabricate, inexpensive, light-weight, and able to operate safely in contact with humans.Chemistry and Chemical Biolog

Coated and uncoated cellophane as materials for microplates and open-channel microfluidics devices

This communication describes the use of uncoated cellophane (regenerated cellulose films) for the fabrication of microplates, and the use of coated cellophane for the fabrication of open-channel microfluidic devices. The microplates based on uncoated cellophane are particularly interesting for applications that require high transparency in the ultraviolet (UV) regime, and offer a low-cost alternative to expensive quartz-well plates. Uncoated cellophane is also resistant to damage by various solvents. The microfluidic devices, based on coated cellophane, can have features with dimensions as small as 500 μm, and complex, non-planar geometries. Electrodes can be printed on the surface of the coated cellophane, and embedded in microfluidic devices, to develop resistive heaters and electroanalytical devices for flow injection analysis, and continuous flow electrochemiluminescence (ECL) applications. These open-channel devices are appropriate for applications where optical transparency (especially in the visible regime), resistance to damage by water, biocompatibility and biodegradability are important. Cellophane microfluidic systems complement existing cellulose-based paper microfluidic systems, and provide an alternative to other materials used in microfluidics, such as synthetic polymers or glass. Cellulose films are plausible materials for uses in integrated microfluidic systems for diagnostics, analyses, cell-culture, and MEMS.Chemistry and Chemical Biolog

Outcomes and treatment strategies for autoimmunity and hyperinflammation in patients with RAG deficiency

BACKGROUND: While autoimmunity and hyperinflammation secondary to recombinase activating gene (RAG) deficiency have been associated with delayed diagnosis and even death, our current understanding is limited primarily to small case series. OBJECTIVE: Understand the frequency, severity, and treatment responsiveness of autoimmunity and hyperinflammation in RAG deficiency. METHODS: In reviewing the literature and our own database, we identified 85 patients with RAG deficiency, reported between 2001 and 2016, and compiled the largest case series to date of 63 patients with prominent autoimmune and/or hyperinflammatory pathology. RESULTS: Diagnosis of RAG deficiency was delayed a median of 5 years from the first clinical signs of immune dysregulation. The majority of patients (55.6%) presented with more than one autoimmune or hyperinflammatory complication, with the most common etiologies being cytopenias (84.1%), granulomas (23.8%), and inflammatory skin disorders (19.0%). Infections, including live viral vaccinations, closely preceded the onset of autoimmunity in 28.6% of cases. Autoimmune cytopenias had early onset (median 1.9, 2.1, and 2.6 years for autoimmune hemolytic anemia (AIHA), immune thrombocytopenia (ITP) and autoimmune neutropenia (AN), respectively) and were refractory to intravenous immunoglobulin, steroids, and rituximab in the majority of cases (64.7%, 73.7%, and 71.4% for AIHA, ITP, and AN, respectively). Evans syndrome specifically was associated with lack of response to first-line therapy. Treatment-refractory autoimmunity/hyperinflammation prompted hematopoietic stem cell transplantation in 20 patients. CONCLUSIONS: Autoimmunity/hyperinflammation can be a presenting sign of RAG deficiency and should prompt further evaluation. Multi-lineage cytopenias are often refractory to immunosuppressive treatment and may require hematopoietic cell transplantation for definitive management

Scanning tunneling microscopy studies of fivefold surfaces of icosahedral Al-Pd-Mn quasicrystals and of thin silver films on those surfaces

Quasicrystals are non-periodic but well-ordered solids. Their unusual atomic structures foster peculiar surface properties such as low friction and enhanced oxidation resistance. This is well established at least for aluminum-rich icosahedral (i) quasicrystals. It is also very well known that sputter-annealed surfaces of i-Al-Pd-Mn possess step-terrace morphology even though a network of Bergman and Mackay clusters defines its bulk structure.;Using scanning tunneling microscope (STM) we have investigated clean fivefold surfaces of i-Al-Pd-Mn quasicrystals. In addition, we have examined the bulk structural models of icosahedral Al-Pd-Mn quasicrystals in terms of the densities, compositions and interplanar spacings for the fivefold planes. We focus on four models that contain no partial or mixed occupancies, but we have made some comparisons to a fifth model containing such sites. Each of the four models contains paired planes (layers) that can be separated into two main families on the basis of three features: the relative densities of the two planes, the gap separating the layer from the nearest atomic plane, and the Pd content in the topmost plane. We have compared these families with the available experimental data obtained for the fivefold surfaces. The experimental data and other arguments lead to the conclusion that the family with no Pd in the top plane is favored.;We have studied the nucleation and growth of Ag islands on the fivefold surface of the i-Al-Pd-Mn quasicrystal using STM. From 127 K to 300 K, the density of Ag islands remains constant but it drops as temperature increases beyond 300 K. To understand this behavior, we have developed a mean field rate equation model that takes into account the enhanced nucleation at traps relative to nucleation at regular terrace sites. The best fit to the model suggests that the critical sizes for the nucleation at both sites are large, especially at the traps, where six Ag atoms form stable clusters, and that binding between Ag atoms at the traps is stronger than at the regular terrace sites. In addition, we have identified these trap sites as the cut clusters in the aforementioned structure analysis.</p