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Biomedical subjects

Jeremy Levy

Publications and source records attributed to Jeremy Levy.

11 recordsLinked to original sources

All-electrical control of single ion spins in a semiconductor.

We propose a method for all-electrical manipulation of single ion spins substituted into a semiconductor. Mn ions with a bound hole in GaAs form a natural example. Direct electrical manipulation of the ion spin is possible, because electric fields manipulate the orbital wave function of the hole, and through the spin-orbit coupling the spin is reoriented as well. Coupling ion spins can be achieved using gates to control the size of the hole wave function. Coherent manipulation of ionic spins may find applications in high-density storage and in scalable coherent or quantum information processing.

Journal Article↗

The chemisorption of coronene on Si(001)-2 x 1.

Coronene (C24H12) adsorption on the clean Si(001)-2 x 1 surface was investigated by scanning tunneling microscopy and by density-functional calculations. The coronene adsorbed randomly at 25 degrees C on the surface and did not form two-dimensional islands. The scanning tunneling microscopy measurements revealed three adsorption sites for the coronene molecule on the Si(001) surface at low coverage. The major adsorption configuration involves coronene bonding to four underlying Si atoms spaced two lattice spacings apart in a dimer row. The two minor adsorption configurations involve asymmetrical bonding of a coronene molecule between Si dimer rows and form surface species with a mirror plane symmetry to their chiral neighbor species. The two minor bonding arrangements are stabilized by a type-C defect on the Si(001) surface.

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GHz apertureless near-field scanning optical microscopy of ferroelectric nanodomain dynamics.

Nanoscale domain dynamics of (Ba,Sr)TiO(3) thin films are investigated at microwave frequencies with a home-developed GHz-frequency apertureless near-field scanning optical microscope (GHz-ANSOM). Using a microwave phase-modulation technique, we decoupled topographic artifacts from the optical signal, providing an enhanced and background-free temporal response. Interleaved acquisition of images taken at sequential time intervals provides amplitude and phase information about the electrooptic response at <50 nm spatial resolution and <10 ps temporal resolution. The local microwave response is highly nonuniform in both the amplitude and the phase.

Journal Article↗

Systemic vasculitis: still a challenging disease.

The efficacy of current therapeutic regimens in patients with systemic vasculitis is high, at the expense of considerable treatment toxicity. Optimal therapy for patients with these potentially life-threatening diseases is still debated. Our increased understanding of the pathogenetic mechanisms of systemic vasculitis has led to the development of new therapeutic alternatives, with better potential specificity for both the inflammation and immunologic causes of vasculitis: new immunosuppressive drugs (mycophenolate), monoclonal antibody modulators of lymphocyte function (rituximab), and cytokine-directed therapies (infliximab and eternacept). The safety and efficacy of such agents increasingly are being investigated in patients with systemic vasculitis. Additionally, many randomized prospective clinical trials have been completed to determine the precise roles for more conventional treatments (cyclophosphamide, azathioprine, and plasma exchange), providing an expanding evidence base to guide therapy in these challenging diseases. There now is clear evidence that duration of cyclophosphamide therapy can be relatively short (3 months), long-term maintenance therapy is needed to avoid relapse (often azathioprine), and patients at relatively greater risk for relapse can be identified. We review the most recent data on the current management of systemic antineutrophil cytoplasmic antibody-associated vasculitis, with emphasis on strategies to improve long-term outcome and reduce treatment toxicity while minimizing the risk for relapse.

Aged↗

Peritoneal dialysis catheter removal for acute peritonitis: a retrospective analysis of factors associated with catheter removal and prolonged postoperative hospitalization.

BACKGROUND: Most patients with acute peritoneal dialysis (PD) peritonitis respond to antibiotic therapy, but a significant minority of patients require surgical catheter removal to eradicate the infection. These patients may experience an adverse postsurgical course. METHODS: We retrospectively analyzed 64 episodes of acute peritonitis requiring PD catheter removal in comparison to 426 episodes treated with antibiotics alone. RESULTS: There were no differences between patients who required PD catheter removal and medically treated patients in sex (62% versus 60% men; P > 0.05), PD modality (31% versus 27% automated PD; P > 0.05), time spent on PD therapy (35 versus 26 months; P > 0.05), or cause of end-stage renal failure. Catheter removal was more likely to occur in elderly (mean age, 61 versus 54 years; P = 0.023) and South Asian patients (38% versus 22%; P = 0.020) and after peritonitis caused by Escherichia coli (16% versus 4%; P = 0.0005), Enterobacter species (5% versus 0.7%; P = 0.031), and Pseudomonas species (5% versus 0.7%; P = 0.031). The most significant correlation with requirement for surgical catheter removal was duration of peritonitis (mean, 7.5 versus 2.8 days; P = 1.3 x 10(-6)). Fifty-three percent of catheter removals resulted in postoperative hospitalization longer than 10 days. Delayed discharges were caused by multiple reasons. Compared with discharges within 10 days, prolonged hospitalization was associated with increased age (mean, 64 versus 58 years; P = 0.028) and delay in time to catheter removal (mean, 7.9 versus 5.3 days; P = 0.027). After catheter removal, only 4% of patients successfully returned to maintenance PD therapy. CONCLUSION: Increased age and duration of peritonitis are associated with both requirement for PD catheter removal and prolonged postoperative hospitalization.

Acute Disease↗

Prospective study of TNFalpha blockade with infliximab in anti-neutrophil cytoplasmic antibody-associated systemic vasculitis.

UNLABELLED: Tumor necrosis factor alpha (TNFalpha) plays an important role in the pathogenesis of anti-neutrophil cytoplasmic antibody-associated systemic vasculitis. TNFalpha blockade is a potential therapy for these disorders. METHODS: An open-label, multi-center, prospective clinical trial in two subgroups was performed. Study I examined acute disease, either first presentation or relapse (Birmingham Vasculitis Activity Score [BVAS] > or = 10; n = 16); study II examined persistent disease (BVAS > or = 4; n = 16). Patients received infliximab (5 mg/kg) at 0, 2, 6, and 10 wk. Concomitant therapy in study I included prednisolone and cyclophosphamide. Study II patients continued their existing treatment regimens, with prednisolone tapered according to clinical status. RESULTS: Mean age was 52.4 yr, 53% of the patients were female, and follow-up was 16.8 mo. Twenty-eight patients (88%) achieved remission (14 per study group). BVAS decreased from 12.3 (confidence interval [CI] = 10.5 to 14.0) at entry to 0.3 (CI = 0.2 to 0.9) at wk 14 (P < 0.001). C-reactive protein (mg/L) decreased from 29.4 (CI = 16.8 to 42.0) at entry to 7.0 (CI = 3.3 to 10.9) by wk 14 (P = 0.001). Mean prednisolone dose (mg/d) in study II decreased from 23.8 (CI = 15.0 to 32.5) at entry to 8.8 (CI = 5.9 to 11.7) at wk 14 (P = 0.002). There were two deaths and seven serious infections. Relapse occurred in five patients (three in study II) after a mean of 27 wk. CONCLUSION: TNFalpha blockade with infliximab was effective at inducing remission in 88% of patients with antibody-associated systemic vasculitis and permitted reduction in steroid doses. Severe infections were seen in 21% of patients, and despite continued infliximab, 20% of initial responders experienced disease flares. Infliximab is a promising new therapy for vasculitis both as a component of initial therapy and in the management of refractory disease. These results need confirmation in larger randomized trials.

Adult↗

Lattice-scale domain wall dynamics in ferroelectrics.

Ferroelectric domain walls are atomically thin, and consequently their dynamics are sensitive to the periodic potential of the underlying lattice. Despite their central role in domain dynamics, lattice-scale effects have never been directly observed. We investigate local domain dynamics in thin film ferroelectrics using atomic-force microscopy. Upon combined dc and ac electric driving, fluctuations in the local piezoresponse are observed. Fourier analysis of the fluctuations reveals the presence of narrow band and broad band noise, and Barkhausen jumps. The narrow band noise is attributed to dynamics associated with lattice-scale pinning and is reproduced by a simple physical model.

Journal Article↗

Quantum computing with spin cluster qubits.

We study the low energy states of finite spin chains with isotropic (Heisenberg) and anisotropic (XY and Ising-like) antiferromagnetic exchange interaction with uniform and nonuniform coupling constants. We show that for an odd number of sites a spin cluster qubit can be defined in terms of the ground state doublet. This qubit is remarkably insensitive to the placement and coupling anisotropy of spins within the cluster. One- and two-qubit quantum gates can be generated by magnetic fields and intercluster exchange, and leakage during quantum gate operation is small. Spin cluster qubits inherit the long decoherence times and short gate operation times of single spins. Control of single spins is hence not necessary for the realization of universal quantum gates.

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Universal quantum computation with spin-1/2 pairs and Heisenberg exchange.

An efficient and intuitive framework for universal quantum computation is presented that uses pairs of spin-1/2 particles to form logical qubits and a single physical interaction, Heisenberg exchange, to produce all gate operations. Only two Heisenberg gate operations are required to produce a controlled pi-phase shift, compared to nineteen for exchange-only proposals employing three spins. Evolved from well-studied decoherence-free subspaces, this architecture inherits immunity from collective decoherence mechanisms. The simplicity and adaptability of this approach should make it attractive for spin-based quantum computing architectures.

Journal Article↗

Local ferroelectricity in SrTiO3 thin films.

The temperature-dependent polarization of SrTiO3 thin films is investigated using confocal scanning optical microscopy. A homogeneous out-of-plane and an inhomogeneous in-plane ferroelectric phase are identified from images of the linear electro-optic response. Both hysteretic and nonhysteretic behavior are observed under a dc bias field. Unlike classical transitions in bulk ferroelectrics, local ferroelectricity is observed at temperatures far above the dielectric permittivity maximum. The results demonstrate the utility of local probe experiments in understanding inhomogeneous ferroelectrics.

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