Insulator-to-Metal Transition in Selenium-Hyperdoped Silicon: Observation and Origin

Hyperdoping has emerged as a promising method for designing semiconductors with unique optical and electronic properties, although such properties currently lack a clear microscopic explanation. Combining computational and experimental evidence, we probe the origin of sub-band gap optical absorption and metallicity in Se-hyperdoped Si. We show that sub-band gap absorption arises from direct defect-to-conduction band transitions rather than free carrier absorption. Density functional theory predicts the Se-induced insulator-to-metal transition arises from merging of defect and conduction bands, at a concentration in excellent agreement with experiment. Quantum Monte Carlo calculations confirm the critical concentration, demonstrate that correlation is important to describing the transition accurately, and suggest that it is a classic impurity-driven Mott transition.Comment: 5 pages, 3 figures (PRL formatted

Atrioventricular conduction in patients undergoing pacemaker implant following self‐expandable transcatheter aortic valve replacement

BackgroundHeart block requiring a pacemaker is common after self‐expandable transcatheter aortic valve replacement (SE‐TAVR); however, conduction abnormalities may improve over time. Optimal device management in these patients is unknown.ObjectiveTo evaluate the long‐term, natural history of conduction disturbances in patients undergoing pacemaker implantation following SE‐TAVR.MethodsAll patients who underwent new cardiac implantable electronic device (CIED) implantation at Michigan Medicine following SE‐TAVR placement between January 1, 2012 and September 25, 2017 were identified. Electrocardiogram and device interrogation data were examined during follow‐up to identify patients with recovery of conduction. Logistic regression analysis was used to compare clinical and procedural variables to predict conduction recovery.ResultsFollowing SE‐TAVR, 17.5% of patients underwent device placement for new atrioventricular (AV) block. Among 40 patients with an average follow‐up time of 17.1 ± 8.1 months, 20 (50%) patients had durable recovery of AV conduction. Among 20 patients without long‐term recovery, four (20%) had transient recovery. The time to transient conduction recovery was 2.2 ± 0.2 months with repeat loss of conduction at 8.2 ± 0.9 months. On multivariate analysis, larger aortic annular size (odds ratio: 0.53 [0.28–0.86]/mm, P = 0.02) predicted lack of conduction recovery.ConclusionsHalf of the patients undergoing CIED placement for heart block following SE‐TAVR recovered AV conduction within several months and maintained this over an extended follow‐up period. Some patients demonstrated transient recovery of conduction before recurrence of conduction loss. Larger aortic annulus diameter was negatively associated with conduction recovery.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/150495/1/pace13694_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/150495/2/pace13694.pd

Measuring the Photon Helicity in Radiative B Decays

We propose a way of measuring the photon polarization in radiative B decays into K resonance states decaying to K\pi\pi, which can test the Standard Model and probe new physics. The photon polarization is shown to be measured by the up-down asymmetry of the photon direction relative to the K\pi\pi decay plane in the K resonance rest frame. The integrated asymmetry in K_1(1400)\to K\pi\pi, calculated to be 0.34\pm 0.05 in the Standard Model, is measurable at currently operating B factories.Comment: 4 pages, final version to appear in Physical Review Letter

Path Crossing Exponents and the External Perimeter in 2D Percolation

2D Percolation path exponents $x^{\cal P}_{\ell}$ describe probabilities for traversals of annuli by $\ell$ non-overlapping paths, each on either occupied or vacant clusters, with at least one of each type. We relate the probabilities rigorously to amplitudes of $O(N=1)$ models whose exponents, believed to be exact, yield $x^{\cal P}_{\ell}=({\ell}^2-1)/12$. This extends to half-integers the Saleur--Duplantier exponents for $k=\ell/2$ clusters, yields the exact fractal dimension of the external cluster perimeter, $D_{EP}=2-x^{\cal P}_3=4/3$, and also explains the absence of narrow gate fjords, as originally found by Grossman and Aharony.Comment: 4 pages, 2 figures (EPSF). Revised presentatio

Surgical Explantation of Transcatheter Aortic Valve Bioprostheses: A Statewide Experience

BACKGROUND: Despite the rapid adoption of transcatheter aortic valve replacement (TAVR) since its initial approval in 2011, the frequency and outcomes of surgical explantation of TAVR devices (TAVR-explant) is poorly understood. METHODS: Patients undergoing TAVR-explant between January 2012 and June 2020 at 33 hospitals in Michigan were identified in the Society of Thoracic Surgeons Database and linked to index TAVR data from the Transcatheter Valve Therapy Registry through a statewide quality collaborative. The primary outcome was operative mortality. Indications for TAVR-explant, contraindications to redo TAVR, operative data, and outcomes were collected from Society of Thoracic Surgeons and Transcatheter Valve Therapy databases. Baseline Society of Thoracic Surgeons Predicted Risk of Mortality was compared between index TAVR and TAVR-explant. RESULTS: Twenty-four surgeons at 12 hospitals performed TAVR-explants in 46 patients (median age, 73). The frequency of TAVR-explant was 0.4%, and the number of explants increased annually. Median time to TAVR-explant was 139 days and among known device types explanted, most were self-expanding valves (29/41, 71%). Common indications for TAVR-explant were procedure-related failure (35%), paravalvular leak (28%), and need for other cardiac surgery (26%). Contraindications to redo TAVR included need for other cardiac surgery (28%), unsuitable noncoronary anatomy (13%), coronary obstruction (11%), and endocarditis (11%). Overall, 65% (30/46) of patients underwent concomitant procedures, including aortic repair/replacement in 33% (n=15), mitral surgery in 22% (n=10), and coronary artery bypass grafting in 16% (n=7). The median Society of Thoracic Surgeons Predicted Risk of Mortality was 4.2% at index TAVR and 9.3% at TAVR-explant (P=0.001). Operative mortality was 20% (9/46) and 76% (35/46) of patients had in-hospital complications. Of patients alive at discharge, 37% (17/37) were discharged home and overall 3-month survival was 73±14%. CONCLUSIONS: TAVR-explant is rare but increasing, and its clinical impact is substantial. As the utilization of TAVR expands into younger and lower-risk patients, providers should consider the potential for future TAVR-explant during selection of an initial valve strategy

Incomplete retention after direct myocardial injection

Direct intramyocardial injection may permit local delivery of protein and gene therapy agents for myocardial and coronary artery disease. Little is known about the immediate fate of materials administered via percutaneous endomyocardial catheters or via surgical epicardial injection. In this study, we use a novel method to evaluate the acute retention of agents injected directly into the myocardium, compare epicardial with the percutaneous endocardial and postmortem delivery, and evaluate the influence of injectate volume on myocardial retention. Fifteen 40–50 kg pigs underwent overlapping myocardial injections using a percutaneous endomyocardial catheter, an epicardial needle via an open chest, and epicardial needle postmortem. Multiple distinct 15 Μ neutron-activated microsphere species were used as tracers. Two or three myocardial walls were injected in each animal using 3.5 mm, 27–28 gauge needles at varying injectate volumes. Animals were sacrificed immediately. Myocardial walls were divided and multiple microsphere species were quantified. In an additional study, nine 70 kg pigs underwent percutaneous endomyocardial injections with replication-deficient adenovirus encoding for the production of lac-Z. The injectate volume was varied, while the viral particle number remained constant. The animals were sacrificed 5 days after the percutaneous injections; the heart, liver, and spleen were collected for Β-galactosidase activity. Endomyocardial injection was associated with 43% ± 15% microsphere retention, compared with 15% ± 21% ( P < 0.01) retention of open chest epicardial injection and 89% ± 60% ( P < 0.01) for postmortem injection. Reducing the injectate volume from 100 to 10 ΜL improved microsphere retention ( P = 0.01). There was a trend toward improved viral transfection associated with smaller injection volumes. Despite direct intramyocardial administration, a significant fraction of injectate is not retained locally. Catheter-based needle endomyocardial injection is associated with equivalent or superior injectate retention compared with open chest epicardial injection. Proportionately, more injectate may be retained at lower volumes. Loss may involve a combination of channel leakage, venous, and lymphatic return. Cathet Cardiovasc Intervent 2002;55:392–397. © 2002 Wiley-Liss, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/35254/1/10136_ftp.pd

Antibodies to C1q in systemic lupus erythematosus: Characteristics and relation to FcγRIIA alleles

Antibodies to C1q in systemic lupus erythematosus: Characteristics and relation to FcγRIIA alleles. Autoantibodies to the collagen-like region of the first complement component (C1qAB) are found in patients with systemic lupus erythematosus (SLE), particularly those with renal disease. In a cohort of 46 SLE patients with diffuse proliferative glomerulonephritis, we found declining C1qAB titers in 77% of treatment responders and in only 38% of treatment non-responders (P < 0.03). To further characterize this autoantibody, we tested 240 SLE patients for the presence of C1qAB. Positive titers were found in 44% of patients with renal disease and 18% of patients without renal disease (χ2 P < 0.0003). Analysis of IgG subclass revealed IgG2 C1qAB alone in 34%, IgG1 C1qAB alone in 20%, and both IgG1 and IgG2 in 46% of patients. Fewer than 10% of patients had measurable titers of IgG3 or IgG4 C1qAB. The pathogenic role of these IgG2-skewed C1qAB may relate to impaired immune complex clearance by the mononuclear phagocyte system: IgG2 antibodies are efficiently recognized by only one IgG receptor, the H131 allele of FcγRIIa (FcγRIIa-H131). In contrast, FcγRIIa-R131, which is characterized by minimal IgG2 binding, has recently been associated with lupus nephritis. In our C1qAB positive patients, the presence of FcγRIIA-R131 was associated with an increased risk for renal disease. Autoantibodies to C1q may have pathogenic significance in SLE patients with genetic defects in the ability to clear IgG2 containing immune complexes

Photon polarization in radiative B decays

We study decay distributions in B -> K pi pi gamma, combining contributions from several overlapping resonances in a K pi pi mass range near 1400 MeV, (1^+) K_1(1400), (2^+) K^*_2(1430) and (1^-) K^*(1410). A method is proposed for using these distributions to determine a photon polarization parameter in the effective radiative weak Hamiltonian. This parameter is measured through an up-down asymmetry of the photon direction relative to the K pi pi decay plane. We calculate a dominant up-down asymmetry of 0.33 +- 0.05 from the K1(1400) resonance, which can be measured with about 10^8 B B-bar pairs, thus providing a new test for the Standard Model and a probe for some of its extensions.Comment: 22 pages, 3 figures, version to appear in Phys. Rev.

Sustained Vascular Endothelial Growth Factor Delivery Enhances Angiogenesis and Perfusion in Ischemic Hind Limb

We hypothesized that sustained delivery of vascular endothelial growth factor (VEGF) using a polymer [85:15 poly(lactide- co -glycolide) (PLG)] would enhance angiogenesis and improve perfusion of ischemic tissue.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41507/1/11095_2005_Article_5644.pd