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1.
Phys Rev Lett ; 110(18): 186805, 2013 May 03.
Artigo em Inglês | MEDLINE | ID: mdl-23683234

RESUMO

We show that the interplay of cyclotron motion and Andreev reflection experienced by massless-Dirac-like charge carriers in topological-insulator surface states generates a Majorana-particle excitation. On the basis of an envelope-function description of the Dirac-Andreev edge states, we discuss the kinematic properties of the Majorana mode and find them to be tunable by changing the superconductor's chemical potential and/or the magnitude of the perpendicular magnetic field. Our proposal opens up new possibilities for studying Majorana fermions in a controllable setup.

2.
Phys Rev Lett ; 110(8): 083605, 2013 Feb 22.
Artigo em Inglês | MEDLINE | ID: mdl-23473146

RESUMO

We propose to use weak measurements away from the weak-value amplification regime to carry out precision measurements of time delays of light. Our scheme is robust to several sources of noise that are shown to only limit the relative precision of the measurement. Thus, they do not set a limit on the smallest measurable phase shift, contrary to standard interferometry and weak-value-based measurement techniques. Our idea is not restricted to phase-shift measurements and could be used to measure other small effects using a similar protocol.

3.
Phys Rev Lett ; 109(12): 126407, 2012 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-23005969

RESUMO

We consider electron-phonon coupling in crystalline organic semiconductors, using naphthalene for our case study. Employing a first-principles approach, we compute the changes in the selfconsistent Kohn-Sham potential corresponding to different phonon modes and go on to obtain the carrier-phonon coupling matrix elements (vertex functions). We then evaluate perturbatively the quasiparticle spectral residues for electrons at the bottom of the lowest unoccupied (LUMO), and holes at the top of the highest occupied (HOMO), band, obtaining Z(e) ≈ 0.74 and Z(h) ≈ 0.78, respectively. Along with the widely accepted notion that the carrier-phonon coupling strengths in polyacenes decrease with increasing molecular size, our results provide strong microscopic evidence for the previously conjectured nonpolaronic nature of bandlike carriers in these systems.

4.
Phys Rev Lett ; 109(25): 250501, 2012 Dec 21.
Artigo em Inglês | MEDLINE | ID: mdl-23368438

RESUMO

We propose an analog quantum simulation of small-polaron physics using a one-dimensional system of trapped ions acted upon by off-resonant standing waves. This system, envisioned as an array of microtraps, in the single-excitation case allows the realization of the antiadiabatic regime of the Holstein model. We show that the strong excitation-phonon coupling regime, characterized by the formation of small polarons, can be reached using realistic values of the relevant system parameters. Finally, we propose measurements of the quasiparticle residue and the average number of phonons in the ground state, experimental probes validating the polaronic character of the phonon-dressed excitation.

5.
Phys Rev Lett ; 107(13): 136403, 2011 Sep 23.
Artigo em Inglês | MEDLINE | ID: mdl-22026879

RESUMO

Domain walls between superconducting and magnetic regions placed on top of a topological insulator support transport channels for Majorana fermions. We propose to study noise correlations in a Hanbury Brown-Twiss type interferometer and find three signatures of the Majorana nature of the channels. First, the average charge current in the outgoing leads vanishes. Furthermore, we predict an anomalously large shot noise in the output ports for a vanishing average current signal. Adding a quantum point contact to the setup, we find a surprising absence of partition noise which can be traced back to the Majorana nature of the carriers.

6.
Phys Rev Lett ; 100(2): 027202, 2008 Jan 18.
Artigo em Inglês | MEDLINE | ID: mdl-18232914

RESUMO

We propose a way to measure the momentum p of a nanomechanical oscillator. The p detector is based on two tunnel junctions in an Aharonov-Bohm-type setup. One of the tunneling amplitudes depends on the motion of the oscillator, the other one not. Although the coupling between the detector and the oscillator is assumed to be linear in the position x of the oscillator, it turns out that the finite-frequency noise output of the detector will in general contain a term proportional to the momentum spectrum of the oscillator. This is a true quantum phenomenon, which can be realized in practice if the phase of the tunneling amplitude of the detector is tuned by the Aharonov-Bohm flux Phi to a p-sensitive value.

7.
Phys Rev Lett ; 99(13): 130403, 2007 Sep 28.
Artigo em Inglês | MEDLINE | ID: mdl-17930560

RESUMO

The Stern-Gerlach effect is well known as spin-dependent splitting of a beam of atoms with magnetic moments by a magnetic-field gradient. Here, we show that an induced gauge potential may lead to a similar effect for chiral molecules. In the presence of three inhomogeneous light fields, the center of mass of a three-level chiral molecule is subject to an optically induced gauge potential, and the internal dynamics of the molecule can be described as an adiabatic evolution in the reduced pseudospin subspace of the two lowest energy levels. We demonstrate numerically that such an induced gauge potential can lead to observable pseudospin-dependent and chirality-dependent generalized Stern-Gerlach effects for mixed left- and right-handed chiral molecules under realistic conditions.

8.
Phys Rev Lett ; 99(8): 086404, 2007 Aug 24.
Artigo em Inglês | MEDLINE | ID: mdl-17930966

RESUMO

We evaluate the Coulomb drag current in two finite-length Tomonaga-Luttinger-liquid wires coupled by an electrostatic backscattering interaction. The drag current in one wire shows oscillations as a function of the bias voltage applied to the other wire, reflecting interferences of the plasmon standing waves in the interacting wires. In agreement with this picture, the amplitude of the current oscillations is reduced with increasing temperature. This is a clear signature of non-Fermi-liquid physics because for coupled Fermi liquids the drag resistance is always expected to increase as the temperature is raised.


Assuntos
Física , Temperatura Ambiente
9.
J Med Genet ; 43(1): 28-38, 2006 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-15944227

RESUMO

BACKGROUND: Segmental duplications flanking the neurofibromatosis type 1 (NF1) gene locus on 17q11 mediate most gene deletions in NF1 patients. However, the large size of the gene and the complexity of the locus architecture pose difficulties in deletion analysis. We report the construction and application of the first NF1 locus specific microarray, covering 2.24 Mb of 17q11, using a non-redundant approach for array design. The average resolution of analysis for the array is approximately 12 kb per measurement point with an increased average resolution of 6.4 kb for the NF1 gene. METHODS: We performed a comprehensive array-CGH analysis of 161 NF1 derived samples and identified heterozygous deletions of various sizes in 39 cases. The typical deletion was identified in 26 cases, whereas 13 samples showed atypical deletion profiles. RESULTS: The size of the atypical deletions, contained within the segment covered by the array, ranged from 6 kb to 1.6 Mb and their breakpoints could be accurately determined. Moreover, 10 atypical deletions were observed to share a common breakpoint either on the proximal or distal end of the deletion. The deletions identified by array-CGH were independently confirmed using multiplex ligation-dependent probe amplification. Bioinformatic analysis of the entire locus identified 33 segmental duplications. CONCLUSIONS: We show that at least one of these segmental duplications, which borders the proximal breakpoint located within the NF1 intron 1 in five atypical deletions, might represent a novel hot spot for deletions. Our array constitutes a novel and reliable tool offering significantly improved diagnostics for this common disorder.


Assuntos
Quebra Cromossômica , Deleção de Genes , Duplicação Gênica , Neurofibromina 1/genética , Mapeamento Cromossômico , Cromossomos Humanos Par 17/genética , Biologia Computacional , Análise Mutacional de DNA , Humanos , Análise de Sequência com Séries de Oligonucleotídeos , Reprodutibilidade dos Testes
10.
Phys Rev Lett ; 92(20): 206801, 2004 May 21.
Artigo em Inglês | MEDLINE | ID: mdl-15169373

RESUMO

We study current fluctuations in an interacting three-terminal quantum dot with ferromagnetic leads. For appropriately polarized contacts, the transport through the dot is governed by dynamical spin blockade, i.e., a spin-dependent bunching of tunneling events not present in the paramagnetic case. This leads, for instance, to positive zero-frequency cross correlations of the currents in the output leads even in the absence of spin accumulation on the dot. We include the influence of spin-flip scattering and identify favorable conditions for the experimental observation of this effect with respect to polarization of the contacts and tunneling rates.

11.
Phys Rev Lett ; 92(5): 056805, 2004 Feb 06.
Artigo em Inglês | MEDLINE | ID: mdl-14995330

RESUMO

We analyze shot noise under the influence of dephasing in an electronic Mach-Zehnder interferometer, of the type that was realized recently [Nature (London) 422, 415 (2003)]]. Using a model of dephasing by a fluctuating classical field, we show how the usual partition noise expression T(1-T) is modified. We study the dependence on the power spectrum of the field, which is impossible in simpler approaches such as the dephasing terminal, against which we compare. We remark on shot noise as a tool to distinguish thermal smearing from genuine dephasing.

12.
Phys Rev Lett ; 91(5): 057003, 2003 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-12906625

RESUMO

We propose and investigate a novel method for the controlled coupling of two Josephson charge qubits by means of a variable electrostatic transformer. The value of the coupling capacitance is given by the discretized curvature of the lowest energy band of a Josephson junction, which can be positive, negative, or zero. We calculate the charging diagram of the two-qubit system that reflects the transition from positive to negative through vanishing coupling. We also discuss how to implement a phase gate making use of the controllable coupling.

13.
Phys Rev Lett ; 91(5): 057005, 2003 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-12906627

RESUMO

We report resonant multiple Andreev reflections in a multiwall carbon nanotube quantum dot coupled to superconducting leads. The position and magnitude of the subharmonic gap structure is found to depend strongly on the level positions of the single-electron states which are adjusted with a gate electrode. We discuss a theoretical model of the device and compare the calculated differential conductance with the experimental data.

14.
Phys Rev E Stat Nonlin Soft Matter Phys ; 66(4 Pt 1): 041111, 2002 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-12443181

RESUMO

We analyze a model of a nonlinear bath consisting of a single two-level system coupled to a linear bath (a classical noise force in the limit considered here). This allows us to study the effects of a nonlinear, non-Markoffian bath in a particularly simple situation. We analyze the effects of this bath onto the dynamics of a spin by calculating the decay of the equilibrium correlator of the z-component of the spin. The exact results are compared with those obtained using three commonly used approximations: a Markoffian master equation for the spin dynamics, a weak-coupling approximation, and the substitution of a linear bath for the original nonlinear bath.

15.
Phys Rev Lett ; 88(19): 197001, 2002 May 13.
Artigo em Inglês | MEDLINE | ID: mdl-12005658

RESUMO

We study the statistics of charge transport in a mesoscopic three-terminal device with one superconducting terminal and two normal-metal terminals. We calculate the full distribution of transmitted charges into the two symmetrically biased normal terminals. In a wide parameter range, we find large positive cross correlations between the currents in the two normal arms. We also determine the third cumulant that provides additional information on the statistics not contained in the current noise.

16.
Phys Rev E Stat Nonlin Soft Matter Phys ; 65(4 Pt 1): 041927, 2002 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-12005893

RESUMO

We consider an experimentally relevant model of a geometric ratchet in which particles undergo drift and diffusive motion in a two-dimensional periodic array of obstacles, and which is used for the continuous separation of particles subject to different forces. The macroscopic drift velocity and diffusion tensor are calculated by a Monte Carlo simulation and by a master-equation approach, using the corresponding microscopic quantities and the shape of the obstacles as input. We define a measure of separation quality and investigate its dependence on the applied force and the shape of the obstacles.

17.
Hum Mol Genet ; 10(3): 271-82, 2001 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-11159946

RESUMO

Neurofibromatosis type 2 (NF2) is an autosomal dominant disorder whose hallmark is bilateral vestibular schwannoma. It displays a pronounced clinical heterogeneity with mild to severe forms. The NF2 tumor suppressor (merlin/schwannomin) has been cloned and extensively analyzed for mutations in patients with different clinical variants of the disease. Correlation between the type of the NF2 gene mutation and the patient phenotype has been suggested to exist. However, several independent studies have shown that a fraction of NF2 patients with various phenotypes have constitutional deletions that partly or entirely remove one copy of the NF2 gene. The purpose of this study was to examine a 7 Mb interval in the vicinity of the NF2 gene in a large series of NF2 patients in order to determine the frequency and extent of deletions. A total of 116 NF2 patients were analyzed using high-resolution array-comparative genomic hybridization (CGH) on an array covering at least 90% of this region of 22q around the NF2 locus. Deletions, which remove one copy of the entire gene or are predicted to truncate the schwannomin protein, were detected in 8 severe, 10 moderate and 6 mild patients. This result does not support the correlation between the type of mutation affecting the NF2 gene and the disease phenotype. This work also demonstrates the general usefulness of the array-CGH methodology for rapid and comprehensive detection of small (down to 40 kb) heterozygous and/or homozygous deletions occurring in constitutional or tumor-derived DNA.


Assuntos
Deleção Cromossômica , DNA/genética , Neurofibromatose 2/genética , Adolescente , Criança , Cromossomos Humanos Par 22/genética , Clonagem Molecular , Mapeamento de Sequências Contíguas , DNA/química , Feminino , Deleção de Genes , Humanos , Hibridização in Situ Fluorescente , Masculino , Proteínas de Membrana/genética , Pessoa de Meia-Idade , Neurofibromatose 2/patologia , Neurofibromina 2 , Hibridização de Ácido Nucleico/métodos , Análise de Sequência de DNA
18.
Hum Genet ; 106(5): 506-16, 2000 May.
Artigo em Inglês | MEDLINE | ID: mdl-10914680

RESUMO

Translocation t(11;22)(q23;q11) is the most common constitutional reciprocal translocation in man. Balanced carriers are phenotypically normal, except for decreased fertility, an increased spontaneous abortion rate and a possible predisposition to breast cancer in some families. Here, we report the high resolution mapping of the t(11;22)(q23;q11) breakpoint. We have localised the breakpoint, by using fluorescence in situ hybidisation (FISH) walking, to a region between D11S1340 and WI-8564 on chromosome 11, and D22S134 and D22S264 on chromosome 22. We report the isolation of a bacterial artificial chromosome (BAC) clone spanning the breakpoint in 11q23. We have narrowed down the breakpoint to an 80-kb sequenced region on chromosome 11 and FISH analysis has revealed a variation of the breakpoint position between patients. In 22q11, we have sequenced two BACs (BAC2280L11 and BAC41C4) apparently mapping to the region; these contain low copy repeats (LCRs). Southern blot analysis with probes from BAC2280L11 has revealed different patterns between normal controls and translocation carriers, indicating that sequences similar/identical to these probes flank the translocation breakpoint. The occurrence of LCRs has previously been associated with genomic instability and "unclonable" regions. Hence, the presence of such repeats renders standard translocation breakpoint cloning techniques ineffective. Thus, we have used high resolution fiber-FISH to study this region in normal and translocation cases by using probes from 22q11, LCRs and 11q23. We demonstrate that the LCR containing the gap in 22q11 is probably substantially larger than the previous estimates of 100 kb. Using fiber-FISH, we have localised the breakpoint in 22q11 to approximately 20-40 kb from the centromeric border of the LCR (i.e. the telomeric end of AC006547) and have confirmed the breakpoint position on 11q23.


Assuntos
Mapeamento Cromossômico/métodos , Cromossomos Humanos Par 11/genética , Cromossomos Humanos Par 22/genética , Translocação Genética , Sequência de Bases , Passeio de Cromossomo , Primers do DNA/genética , Sondas de DNA/genética , Feminino , Humanos , Hibridização in Situ Fluorescente , Masculino , Dados de Sequência Molecular , Telômero/genética
19.
Hum Genet ; 104(5): 418-24, 1999 May.
Artigo em Inglês | MEDLINE | ID: mdl-10394935

RESUMO

Schwannomas are tumors arising mainly at cranial and spinal nerves. Bilateral vestibular schwannoma is the hallmark of neurofibromatosis type2 (NF2). The NF2 gene has been cloned and comprehensive analysis of its mutations in schwannomas shows that up to 60% of tumors carry inactivating mutations. Thus, the genetic mechanism behind the development of more than 40% of schwannomas without NF2 mutations is unknown. We have therefore studied tumor tissue from 50 human schwannomas by allelotyping and have found chromosome 22 deletions in over 80% of the cases. We detected 14 cases (27%) that revealed partial deletions of one copy of chromosome 22, i.e., terminal and/or interstitial deletions. We sequenced the NF2 gene in seven of these tumors and detected only one case with mutations. The deletion mapping of chromosome 22 in tumors with partial deletions indicates that several regions, in addition to the NF2 locus, harbor genes involved in schwannoma tumorigenesis. Our findings suggest that heterogeneity in the mechanisms leading to the development of schwannomas probably exists. These findings are in agreement with the recent analysis of schwannomas from familial and sporadic cases of schwannomatosis and point to a possible role of an additional gene, which, in cooperation with the NF2 tumor suppressor, causes schwannomas.


Assuntos
Deleção Cromossômica , Cromossomos Humanos Par 22 , Genes da Neurofibromatose 2 , Neurilemoma/genética , Adolescente , Adulto , Idoso , Mapeamento Cromossômico , DNA/sangue , Feminino , Marcadores Genéticos , Humanos , Perda de Heterozigosidade , Masculino , Pessoa de Meia-Idade , Neurilemoma/sangue , Neurilemoma/patologia , Neurofibromatose 1/genética , Neurofibromatose 2/genética , Polimorfismo de Fragmento de Restrição
20.
Genes Chromosomes Cancer ; 25(2): 184-90, 1999 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-10338003

RESUMO

Neurofibromatosis type 2 (NF2) is an autosomal dominant disorder predisposing to multiple neoplastic lesions with the hallmark of schwannoma arising at the eighth cranial nerve. NF2 shows a distinct clinical variability, with a mild and a severe form of the disease. The NF2 gene is mutated in constitutional DNA of affected patients from NF2 families and in sporadic cases. Comprehensive mutation analyses in patients with severe and mild phenotypes revealed mutations in only 34%-66%. In the remaining fraction, the genetic mechanism behind the development of NF2 is unknown. Analyses of germline mutations do not provide a conclusive explanation for the observed clinical heterogeneity of NF2. It can therefore be hypothesized that other factors, e.g., modifier gene(s), contribute to the development of a more severe NF2 phenotype. We report a mentally retarded patient with the severe form of NF2 who displays a 7.4 million base pair deletion on chromosome 22. We performed a full genetic characterization of this case using heterozygozity analysis of 41 markers from chromosome 22, detailed FISH mapping of deletion breakpoints, allelotyping of all other chromosomes, and sequencing of the NF2 gene in tumor DNA. Two genomically large deletions similar in size (700-800 kb), which encompass the entire NF2 gene, have been reported previously in mildly affected NF2 patients. The centromeric breakpoints of these deletions were similar to the centromeric breakpoint in the present case. However, the deletion in our patient extends over a much larger distance toward the telomere of 22q. Our results support the existence of NF2 modifier gene(s) and suggest that such a putative locus maps to a 6.5-MB interval on 22q, between D22S32 and the MB gene.


Assuntos
Deleção Cromossômica , Cromossomos Humanos Par 22/genética , Genes da Neurofibromatose 2/genética , Neurofibromatose 2/genética , Adulto , Criança , Genes da Neurofibromatose 2/fisiologia , Marcadores Genéticos , Humanos , Masculino , Fenótipo , Polimorfismo de Fragmento de Restrição
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