Hall carrier density and magnetoresistance measurements in thin film vanadium dioxide across the metal-insulator transition

Temperature dependent magneto-transport measurements in magnetic fields of up to 12 Tesla were performed on thin film vanadium dioxide (VO2) across the metal-insulator transition (MIT). The Hall carrier density increases by 4 orders of magnitude at the MIT and accounts almost entirely for the resistance change. The Hall mobility varies little across the MIT and remains low, ~0.1cm2/V sec. Electrons are found to be the major carriers on both sides of the MIT. Small positive magnetoresistance in the semiconducting phase is measured

Does the degree of preoperative mitral regurgitation predict survival or the need for mitral valve repair or replacement in patients with anomalous origin of the left coronary artery from the pulmonary artery?

BackgroundAnomalous origin of the left coronary artery from the pulmonary artery causes severe myocardial ischemia, global left ventricular dysfunction, and annular dilatation producing varying degrees of mitral regurgitation. Mitral regurgitation secondary to the left ventricular or papillary muscle dysfunction in infants will usually improve in the absence of ongoing ischemia. The aim of this study is to determine the influence of the degree of preoperative mitral regurgitation on the early and late outcomes of patients with anomalous origin of the left coronary artery from the pulmonary artery who underwent coronary reimplantation.MethodsTwenty-five patients underwent coronary reimplantation and 1 early patient had ligation during a 30-year period (median age, 4 months; range, 1 month to 16 years), with a median follow-up of 7 years (range, 4 months to 25 years). Before repair, 7 infants (27%) presented in extremis requiring ventilatory and inotropic support, and 17 patients (65%) presented with heart failure. Mitral regurgitation was present in all patients: trivial in 6 patients, mild in 12 patients, moderate in 5 patients, and severe in 3 patients. No patient underwent mitral valve repair or replacement at the time of anomalous origin of the left coronary artery from the pulmonary artery repair.ResultsHospital survival was 92%. Three patients underwent mitral valve repair or replacement at the mean time of 3.5 years (all with severe preoperative mitral regurgitation). The degree of mitral regurgitation gradually improved in all remaining patients with preoperative mild and moderate mitral regurgitation. Echocardiographic studies demonstrated improvement in left ventricular function in all children. None of the patients showed any evidence of supravalvar pulmonary stenosis as a result of their pulmonary artery reconstruction.ConclusionLong-term clinical outcome and left ventricular function are good despite severe left ventricular dysfunction at presentation. Mitral valve repair or replacement is generally not necessary at the time of anomalous origin of the left coronary artery from the pulmonary artery repair. Significant residual mitral regurgitation is present in some patients and can usually be managed surgically at a later date depending on its degree of severity

Anterior pericardial tracheoplasty for long-segment tracheal stenosis: Long-term outcomes

ObjectiveAlthough several techniques have been described for the treatment of tracheal stenosis, including slide tracheoplasty, tracheal autograft, rib grafting, and use of a pericardial patch, the optimal repair remains controversial because of a lack of long-term follow-up data. The purpose of this study is to examine the long-term results of anterior pericardial tracheoplasty.MethodsTo assess the long-term outcomes of patients who underwent repair of tracheal stenosis with anterior pericardial tracheoplasty, we reviewed the case histories of 26 consecutive patients (1984–present). All but 5 had long-segment tracheal stenosis with more than 10 complete tracheal rings. Twenty-one had significant cardiac disease, and 10 had their cardiac lesions repaired at the time of their tracheoplasty. The median age was 6 months (range, 2 days–25 years). All patients underwent anterior pericardial tracheoplasty through a median sternotomy during normothermic cardiopulmonary bypass. We have previously described our tracheoplasty technique. An average of 14 tracheal rings (range, 5–22) was divided anteriorly, and a patch of fresh autologous pericardium was used to enlarge the trachea to 1.5 times the predicted diameter for age and weight.ResultsThere were 3 hospital deaths (at 1, 2, and 7 months, respectively) and 2 late deaths (at 2 and 13 years postoperatively, respectively). No deaths were related to airway obstruction. Two survivors required tracheostomy postoperatively, one after formation of granulation tissue and stenosis and the other after failure to wean from mechanical ventilation. All survivors remain asymptomatic, with minimal to no evidence of airway obstruction. Median follow-up is 11 years (range, 3 months–22 years).ConclusionAnterior pericardial tracheoplasty for tracheal stenosis provides excellent results in the majority of patients at long-term follow-up

Outcomes in patients with interrupted aortic arch and associated anomalies: a 20-year experience

Objective: The surgical results for the repair of interrupted aortic arch (IAA) have evolved in recent years. We report our results for staged repair of this complex congenital malformation. Methods: Sixty-five patients (mean age, 16.9 ± 41.7 days) were diagnosed with IAA and referred for surgical therapy. The surgical management strategy at our institution between 1982 and 2005 has been one-stage complete repair (n = 13) or staged repair (n = 52) in selected patients. Non-complex patients (group I, n = 51) had a ventricular septal defect (87%), aortopulmonary window (8%), and left ventricular outflow tract obstruction (27%). Group II (n = 14) were patients with Taussig–Bing double outlet right ventricle (n = 6) or truncus arteriosus (n = 8). Method of staged repair of IAA was to transect and turn down the left carotid artery and anastomosis it to the descending aorta (n = 41) or graft interposition (n = 2) combined with a pulmonary artery (PA) banding followed in a few months by delayed ventricular septal defect (VSD) closure and PA de-banding. Results: There were 5 early and 10 late deaths. The actuarial survival including early mortality was 92% at 1 year, 81% at 5 years, and 76% at 10 and 15 years. There was an 81% 15-year survival for children in group I compared with a 54% for children in group II (p ≪ 0.001). Risk factors for increased mortality by univariate analysis were as follows: (1) primary aortic anastomosis (p = 0.03), (2) presence of complex anomalies (p = 0.05), and (3) initial IAA repair performed before 1994 (p = 0.05). Actuarial freedom from any type of aortic reoperation or intervention was 86% at 1 year, 69% at 5 years, and 60% at 10 and 15 years. Univariate and multivariate analyses identified no tested variables as risk factors for reoperation. The majority (86%) was in New York Heart Association (NYHA) class I, and 14% remained in NYHA class II. During the postoperative course there were no neurologic deficits, seizures, and growth disturbances in any patient. Conclusion: Staged repair of IAA using a left carotid artery turn down can be safely applied in IAA patients with and without other intracardiac anomalies with good results. Use of the left carotid artery for arch reconstruction did not result in any detectable neurological events or growth disturbances later in life. Associated anomalies played an important role in outcomes. The long-term probability for reoperation and/or reintervention remains high regardless of operative technique

High-Temperature Hall Effect in Ga(1-x)Mn(x)As

The temperature dependence of the Hall coefficient of a series of ferromagnetic Ga(1-x)Mn(x)As samples is measured in the temperature range 80K < T < 500K. We model the Hall coefficient assuming a magnetic susceptibility given by the Curie-Weiss law, a spontaneous Hall coefficient proportional to rho_xx^2(T), and including a constant diamagnetic contribution in the susceptibility. For all low resistivity samples this model provides excellent fits to the measured data up to T=380K and allows extraction of the hole concentration (p). The calculated p are compared to alternative methods of determining hole densities in these materials: pulsed high magnetic field (up to 55 Tesla) technique at low temperatures (less than the Curie temperature), and electrochemical capacitance- voltage profiling. We find that the Anomalous Hall Effect (AHE) contribution to rho_xy is substantial even well above the Curie temperature. Measurements of the Hall effect in this temperature regime can be used as a testing ground for theoretical descriptions of transport in these materials. We find that our data are consistent with recently published theories of the AHE, but they are inconsistent with theoretical models previously used to describe the AHE in conventional magnetic materials.Comment: 6 pages, 5 figures, 1 table. Accepted to Phys.Rev.

Creation of multiple nanodots by single ions

In the challenging search for tools that are able to modify surfaces on the nanometer scale, heavy ions with energies of several 10 MeV are becoming more and more attractive. In contrast to slow ions where nuclear stopping is important and the energy is dissipated into a large volume in the crystal, in the high energy regime the stopping is due to electronic excitations only. Because of the extremely local (< 1 nm) energy deposition with densities of up to 10E19 W/cm^2, nanoscaled hillocks can be created under normal incidence. Usually, each nanodot is due to the impact of a single ion and the dots are randomly distributed. We demonstrate that multiple periodically spaced dots separated by a few 10 nanometers can be created by a single ion if the sample is irradiated under grazing angles of incidence. By varying this angle the number of dots can be controlled.Comment: 12 pages, 6 figure

Diamond field-effect transistors with V2O5-induced transfer doping: scaling to 50-nm gate length

We report on the fabrication and measurement of hydrogen-terminated diamond field-effect transistors (FETs) incorporating V2O5 as a surface acceptor material to induce transfer doping. Comparing a range of gate lengths down to 50 nm, we observe inversely scaling peak output current and transconductance. Devices exhibited a peak drain current of ~700 mA/mm and a peak transconductance of ~150 mS/mm, some of the highest reported thus far for a diamond metal semiconductor FET (MESFET). Reduced sheet resistance of the diamond surface after V2O5 deposition was verified by four probe measurement. These results show great potential for improvement of diamond FET devices through scaling of critical dimensions and adoption of robust transition metal oxides such as V2O5

Development and characterisation of a large diameter decellularised vascular allograft

The aims of this study were to develop a biological large diameter vascular graft by decellularisation of native human aorta to remove the immunogenic cells whilst retaining the essential biomechanical, and biochemical properties for the ultimate benefit of patients with infected synthetic grafts. Donor aortas (n = 6) were subjected to an adaptation of a propriety decellularisation process to remove the cells and acellularity assessed by histological analysis and extraction and quantification of total DNA. The biocompatibility of the acellular aortas was determined using standard contact cytotoxicity tests. Collagen and denatured collagen content of aortas was determined and immunohistochemistry was used to determine the presence of specific extracellular matrix proteins. Donor aortas (n = 6) were divided into two, with one half subject to decellularisation and the other half retained as native tissue. The native and decellularised aorta sections were then subject to uniaxial tensile testing to failure [axial and circumferential directions] and suture retention testing. The data was compared using a paired t-test. Histological evaluation showed an absence of cells in the treated aortas and retention of histoarchitecture including elastin content. The decellularised aortas had less than 15 ng mg¯¹ total DNA per dry weight (mean 94% reduction) and were biocompatible as determined by in vitro contact cytotoxicity tests. There were no gross changes in the histoarchitecture [elastin and collagen matrix] of the acellular aortas compared to native controls. The decellularisation process also reduced calcium deposits within the tissue. The uniaxial tensile and suture retention testing revealed no significant differences in the material properties (p > 0.05) of decellularised aorta. The decellularisation procedure resulted in minimal changes to the biological and biomechanical properties of the donor aortas. Acellular donor aorta has excellent potential for use as a large diameter vascular graft

The epitaxy of 2D materials growth

Two dimensional (2D) materials consist of one to a few atomic layers, where the intra-layer atoms are chemically bonded and the atomic layers are weakly bonded. The high bonding anisotropicity in 2D materials make their growth on a substrate substantially different from the conventional thin film growth. Here, we proposed a general theoretical framework for the epitaxial growth of a 2D material on an arbitrary substrate. Our extensive density functional theory (DFT) calculations show that the propagating edge of a 2D material tends to align along a high symmetry direction of the substrate and, as a conclusion, the interplay between the symmetries of the 2D material and the substrate plays a critical role in the epitaxial growth of the 2D material. Based on our results, we have outlined that orientational uniformity of 2D material islands on a substrate can be realized only if the symmetry group of the substrate is a subgroup of that of the 2D material. Our predictions are in perfect agreement with most experimental observations on 2D materials&apos; growth on various substrates known up to now. We believe that this general guideline will lead to the large-scale synthesis of wafer-scale single crystals of various 2D materials in the near future. Advances in our ability to manipulate genetics leads to deeper understanding of biological systems. In this perspective, the authors argue that synthetic genomics facilitates complex modifications that open up new areas of research