IMPATT oscillators with enhanced leakage current

The behavior of IMPATT oscillators with enhanced leakage current has been experimentally evaluated by irradiating operating diodes with transient ionizing radiation. Leakage current was induced in diffused junction GaAs and silicon X-band IMPATT diodes by irradiation with 100 nsec pulses of 10 MeV electrons. With increasing leakage current, the oscillator RF power decreases and the frequency of oscillation increases. A large signal circuit model of the IMPATT diode is developed which correlates well with experimental measurements.     

ChIP-Seq-Based Approach in Mouse Enteric Precursor Cells Reveals New Potential Genes with a Role in Enteric Nervous System Development and Hirschsprung Disease

Hirschsprung disease (HSCR) is a neurocristopathy characterized by intestinal aganglionosis which is attributed to a failure in neural crest cell (NCC) development during the embryonic stage. The colonization of the intestine by NCCs is a process finely controlled by a wide and complex gene regulatory system. Several genes have been associated with HSCR, but many aspects still remain poorly understood. The present study is focused on deciphering the PAX6 interaction network during enteric nervous system (ENS) formation. A combined experimental and computational approach was performed to identify PAX6 direct targets, as well as gene networks shared among such targets as potential susceptibility factors for HSCR. As a result, genes related to PAX6 either directly (RABGGTB and BRD3) or indirectly (TGFB1, HRAS, and GRB2) were identified as putative genes associated with HSCR. Interestingly, GRB2 is involved in the RET/GDNF/GFRA1 signaling pathway, one of the main pathways implicated in the disease. Our findings represent a new contribution to advance in the knowledge of the genetic basis of HSCR. The investigation of the role of these genes could help to elucidate their implication in HSCR onset.     

A Multi-Strategy Sequencing Workflow in Inherited Retinal Dystrophies: Routine Diagnosis,Addressing Unsolved Cases and Candidate Genes Identification

The management of unsolved inherited retinal dystrophies (IRD) cases is challenging since no standard pipelines have been established. This study aimed to define a diagnostic algorithm useful for the diagnostic routine and to address unsolved cases. Here, we applied a Next-Generation Sequencing-based workflow, including a first step of panel sequencing (PS) followed by clinical-exome sequencing (CES) and whole-exome sequencing (WES), in 46 IRD patients belonging to 42 families. Twenty-six likely causal variants in retinal genes were found by PS and CES. CES and WES allowed proposing two novel candidate loci (WDFY3 and a X-linked region including CITED1), both abundantly expressed in human retina according to RT-PCR and immunohistochemistry. After comparison studies, PS showed the best quality and cost values, CES and WES involved similar analytical efforts and WES presented the highest diagnostic yield. These results reinforce the relevance of panels as a first step in the diagnostic routine and suggest WES as the next strategy for unsolved cases, reserving CES for the simultaneous study of multiple conditions. Standardizing this algorithm would enhance the efficiency and equity of clinical genetics practice. Furthermore, the identified candidate genes could contribute to increase the diagnostic yield and expand the mutational spectrum in these disorders.     

Conceptual Difficulties Experienced by Trained Engineers Learning Educational Research Methods

This paper describes conceptual difficulties that may be experienced by engineering faculty as they become engineering education researchers. Observation, survey, and assessment data collected at the 2005 NSF‐funded Rigorous Research in Engineering Education workshop were systematically analyzed to uncover the five difficulties encountered by engineering faculty learning to design rigorous education studies: (1) framing research questions with broad appeal, (2) grounding research in a theoretical framework, (3) fully considering operationalization and measurement of constructs, (4) appreciating qualitative or mixed‐methods approaches, and (5) pursuing interdisciplinary collaboration. The first four can be understood in terms of disciplinary consensus; they represent explicit steps in education research that are implicit in technical engineering research because there is greater consensus of methods and standards. This work better frames the issue of rigor in engineering education research by clarifying the fundamental differences that prevent application of traditional engineering standards of rigor directly to engineering education research.     

Oxidative Stress and DNA Damage in Human Gastric Carcinoma: 8-Oxo-7′8-dihydro-2′-deoxyguanosine (8-oxo-dG) as a Possible Tumor Marker

We characterized the oxidative stress (OS) status by the levels of reduced/oxidized glutathione (GSH/GSSG), malondialdehyde (MDA) and the mutagenic base 8-oxo-7′8-dihydro-2′-deoxyguanosine (8-oxo-dG) in human gastric carcinoma (HGC) samples and compared the results with normal tissue from the same patients. We also analyzed 8-oxo-dG in peripheral mononuclear cells (PMNC) and urine from healthy control subjects and in affected patients in the basal state and one, three, six, nine and twelve months after tumor resection. The levels of DNA repair enzyme mRNA expression (hOGG1, RAD51, MUYTH and MTH1) were determined in tumor specimens and compared with normal mucosa. Tumor specimens exhibited increased levels of MDA and 8-oxo-dG compared with normal gastric tissue. GSH levels were also increased, while GSSG levels remained stable. DNA repair enzyme mRNA expression was induced in the tumor tissues. Levels of 8-oxo-dG were significantly elevated in both urine and PMNC of gastric cancer patients compared with healthy controls. After gastrectomy, the levels of the damaged base in urine and PMNC decreased progressively to values close to those found in the healthy population. The high levels of 8-oxo-dG in urine may be related to the increased induction of DNA repair activity in tumor tissue, and the changes observed after tumor resection support its potential use as a tumor marker.     

Fabrication of p-n junction GaAs solar cells by a novel method

p⁺-n diffused junction GaAs solar cells have been successfully fabricated using a novel method in which the diffusion source, anti-reflective coating and protective cover layer are all formed in a single chemical vapor deposition run. The advantage of this process lies in its simple, low cost fabrication procedure and in the fact that the GaAs surface is protected throughout the fabrication procedure.     

Avalanche diode structures suitable for microwave-optical interactions

The r.f. performance of avalanche diode structures with an etched optical window at the top contact has been evaluated. Diode Q and r.f. oscillator tests in X-band IMPATT and S-band TRAPATT silicon diodes show that the optical window does not introduce appreciable series resistance nor degrade oscillator performance.