848 research outputs found

    Uniaxial Phase Transition in Si : Ab initio Calculations

    Full text link
    Based on a previously proposed thermodynamic analysis, we study the relative stabilities of five Si phases under uniaxial compression using ab initio methods. The five phases are diamond, beta-tin, sh, sc, and hcp structures. The possible phase-transition patterns were investigated by considering the phase transitions between any two chosen phases of the five phases. By analyzing the different conributions to the relative pahse stability, we identified the most important factors in reducing the phase-transition pressures at uniaxial compression. We also show that it is possible to have phase transitions occur only when the phases are under uniaxial compression, in spite of no phase transition when under hydrostatic commpression. Taking all five phases into consideration, the phase diagram at uniaxial compression was constructed for pressures under 20 GPa. The stable phases were found to be diamond, beta-tin and sh structures, i.e. the same as those when under hydrostatic condition. According to the phase diagram, direct phase transition from the diamond to the sh phase is possible if the applied uniaxial pressures, on increasing, satisfy the condition of Px>Pz. Simiilarly, the sh-to-beta-tin transition on increeasing pressures is also possible if the applied uniaxial pressures are varied from the condition of Px>Pz, on which the phase of sh is stable, to that of Px<Pz, on which the beta-tin is stable

    Quadratic forms of dimension 8 with trivial discrimiand and Clifford algebra of index 4

    Full text link
    Izhboldin and Karpenko proved in 2000 that any quadratic form of dimension 8 with trivial discriminant and Clifford algebra of index 4 is isometric to the transfer, with respect to some quadratic \'etale extension, of a quadratic form similar to a 2-fold Pfister form. We give a new proof of this result, based on a theorem of decomposability for degree 8 and index 4 algebras with orthogonal involution

    Understanding Anthropological Understanding: for a merological anthropology

    Get PDF
    In this paper I argue for a merological anthropology in which ideas of ‘partiality’ and ‘practical adequacy’ provide a way out of the impasse of relativism which is implied by post-modernism and the related abandonment of a concern with ‘truth’. Ideas such as ‘aptness’ and ‘faithfulness’ enable us to re-establish empirical foundations without having to espouse a simple realism which has been rightly criticised. Ideas taken from ethnomethodology, particularly the way we bootstrap from ‘practical adequacy’ to ‘warrants for confidence’ point to a merological anthropology in which we recognize that we do not and cannot know everything, but that we can have reasons for being confident in the little we know

    The Society for Immunotherapy of Cancer consensus statement on immunotherapy for the treatment of squamous cell carcinoma of the head and neck (HNSCC)

    Get PDF
    Head and neck cancers, including those of the lip and oral cavity, nasal cavity, paranasal sinuses, oropharynx, larynx and nasopharynx represent nearly 700,000 new cases and 380,000 deaths worldwide per annum, and account for over 10,000 annual deaths in the United States alone. Improvement in outcomes are needed for patients with recurrent and or metastatic squamous cell carcinoma of the head and neck (HNSCC). In 2016, the US Food and Drug Administration (FDA) granted the first immunotherapeutic approvals - the anti-PD-1 immune checkpoint inhibitors nivolumab and pembrolizumab - for the treatment of patients with recurrent squamous cell carcinoma of the head and neck (HNSCC) that is refractory to platinum-based regimens. The European Commission followed in 2017 with approval of nivolumab for treatment of the same patient population, and shortly thereafter with approval of pembrolizumab monotherapy for the treatment of recurrent or metastatic HNSCC in adults whose tumors express PD-L1 with a 65 50% tumor proportion score and have progressed on or after platinum-containing chemotherapy. Then in 2019, the FDA granted approval for PD-1 inhibition as first-line treatment for patients with metastatic or unresectable, recurrent HNSCC, approving pembrolizumab in combination with platinum and fluorouracil for all patients with HNSCC and pembrolizumab as a single agent for patients with HNSCC whose tumors express a PD-L1 combined positive score 65 1. These approvals marked the first new therapies for these patients since 2006, as well as the first immunotherapeutic approvals in this disease. In light of the introduction of these novel therapies for the treatment of patients with head and neck cancer, The Society for Immunotherapy of Cancer (SITC) formed an expert committee tasked with generating consensus recommendations for emerging immunotherapies, including appropriate patient selection, therapy sequence, response monitoring, adverse event management, and biomarker testing. These consensus guidelines serve as a foundation to assist clinicians' understanding of the role of immunotherapies in this disease setting, and to standardize utilization across the field for patient benefit. Due to country-specific variances in approvals, availability and regulations regarding the discussed agents, this panel focused solely on FDA-approved drugs for the treatment of patients in the U.S

    Gadoxetate-enhanced abbreviated MRI is highly accurate for hepatocellular carcinoma screening.

    Get PDF
    The primary objective was to compare the performance of 3 different abbreviated MRI (AMRI) sets extracted from a complete gadoxetate-enhanced MRI obtained for hepatocellular carcinoma (HCC) screening. Secondary objective was to perform a preliminary cost-effectiveness analysis, comparing each AMRI set to published ultrasound performance for HCC screening in the USA. This retrospective study included 237 consecutive patients (M/F, 146/91; mean age, 58 years) with chronic liver disease who underwent a complete gadoxetate-enhanced MRI for HCC screening in 2017 in a single institution. Two radiologists independently reviewed 3 AMRI sets extracted from the complete exam: non-contrast (NC-AMRI: T2-weighted imaging (T2wi)+diffusion-weighted imaging (DWI)), dynamic-AMRI (Dyn-AMRI: T2wi+DWI+dynamic T1wi), and hepatobiliary phase AMRI (HBP-AMRI: T2wi+DWI+T1wi during the HBP). Each patient was classified as HCC-positive/HCC-negative based on the reference standard, which consisted in all available patient data. Diagnostic performance for HCC detection was compared between sets. Estimated set characteristics, including historical ultrasound data, were incorporated into a microsimulation model for cost-effectiveness analysis. The reference standard identified 13/237 patients with HCC (prevalence, 5.5%; mean size, 33.7 ± 30 mm). Pooled sensitivities were 61.5% for NC-AMRI (95% confidence intervals, 34.4-83%), 84.6% for Dyn-AMRI (60.8-95.1%), and 80.8% for HBP-AMRI (53.6-93.9%), without difference between sets (p range, 0.06-0.16). Pooled specificities were 95.5% (92.4-97.4%), 99.8% (98.4-100%), and 94.9% (91.6-96.9%), respectively, with a significant difference between Dyn-AMRI and the other sets (p &lt; 0.01). All AMRI methods were effective compared with ultrasound, with life-year gain of 3-12 months against incremental costs of US$ &lt; 12,000. NC-AMRI has limited sensitivity for HCC detection, while HBP-AMRI and Dyn-AMRI showed excellent sensitivity and specificity, the latter being slightly higher for Dyn-AMRI. Cost-effectiveness estimates showed that AMRI is effective compared with ultrasound. • Comparison of different abbreviated MRI (AMRI) sets reconstructed from a complete gadoxetate MRI demonstrated that non-contrast AMRI has low sensitivity (61.5%) compared with contrast-enhanced AMRI (80.8% for hepatobiliary phase AMRI and 84.6% for dynamic AMRI), with all sets having high specificity. • Non-contrast and hepatobiliary phase AMRI can be performed in less than 14 min (including set-up time), while dynamic AMRI can be performed in less than 17 min. • All AMRI sets were cost-effective for HCC screening in at-risk population in comparison with ultrasound

    Possible Role of Meckel's Scan Fused with SPECT CT Imaging: Unraveling the Cause of Abdominal Pain and Obscure-Overt Gastrointestinal Bleeding

    Get PDF
    A 27-year-old male presented with recurrent abdominal pain and high volume hematochezia despite undergoing extensive testing and a right hemicolectomy 3 years prior for a linear bleeding ulceration in the ascending colon. Studies at the University of Michigan included esophagogastroduodenoscopy (EGD), colonoscopy and video capsule endoscopy (VCE), revealing an arteriovenous malformation (AVM) in the terminal ileum. He was hospitalized for recurrent symptoms. His presentation suggested a small bowel source of obscure-overt GI bleeding based on prior non-diagnostic colonoscopy and EGD and a bilious nasogastric lavage. Tagged red blood cell scan localized bleeding to the right lower quadrant. Colonoscopy showed fresh blood in the terminal ileum without a clear source. Angiography showed no evidence of bleeding or terminal ileal AVM. A novel Meckel's scan fused with SPECT imaging showed focal uptake in the terminal ileum. The patient underwent Meckel's diverticulectomy with sparing of adjacent bowel and has remained asymptomatic for 19 months. This case illustrates that patients with obscure-overt GI bleeding require a step-wise multi-modality diagnostic work-up. Because Meckel's scans are false-positive in 28% of adults, Meckel's scan fused with SPECT imaging may offer an approach to refine diagnostic accuracy of either scan alone, but requires further investigation. Exploratory laparotomy should be reserved as a last option and is best performed with intraoperative endoscopy

    The First VERITAS Telescope

    Full text link
    The first atmospheric Cherenkov telescope of VERITAS (the Very Energetic Radiation Imaging Telescope Array System) has been in operation since February 2005. We present here a technical description of the instrument and a summary of its performance. The calibration methods are described, along with the results of Monte Carlo simulations of the telescope and comparisons between real and simulated data. The analysis of TeV γ\gamma-ray observations of the Crab Nebula, including the reconstructed energy spectrum, is shown to give results consistent with earlier measurements. The telescope is operating as expected and has met or exceeded all design specifications.Comment: Accepted by Astroparticle Physic
    corecore