RESUMEN
The identification of electronic entanglement in solids remains elusive so far, which is owed to the difficulty of implementing spinor-selective beam splitters with tunable polarization direction. Here, we propose to overcome this obstacle by producing and detecting a particular type of entanglement encoded in the Nambu spinor or electron-hole components of quasiparticles excited in quantum Hall edge states. Because of the opposite charge of electrons and holes, the detection of the Nambu spinor translates into a charge-current measurement, which eliminates the need for beam splitters and assures a high detection rate. Conveniently, the spinor correlation function at fixed effective polarizations derives from a single current-noise measurement, with the polarization directions of the detector easily adjusted by coupling the edge states to a voltage gate and a superconductor, both having been realized in experiments. We show that the violation of Bell inequality occurs in a large parameter region. Our Letter opens a new route for probing quasiparticle entanglement in solid-state physics exempt from traditional beam splitters.
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Twisted graphene bilayers provide a versatile platform to engineer metamaterials with novel emergent properties by exploiting the resulting geometric moiré superlattice. Such superlattices are known to host bulk valley currents at tiny angles (α≈0.3°) and flat bands at magic angles (α≈1°). We show that tuning the twist angle to α^{*}≈0.8° generates flat bands away from charge neutrality with a triangular superlattice periodicity. When doped with ±6 electrons per moiré cell, these bands are half-filled and electronic interactions produce a symmetry-broken ground state (Stoner instability) with spin-polarized regions that order ferromagnetically. Application of an interlayer electric field breaks inversion symmetry and introduces valley-dependent dispersion that quenches the magnetic order. With these results, we propose a solid-state platform that realizes electrically tunable strong correlations.
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Measuring the ac magnetic response of a type II superconductor provides valuable information on the pinning landscape (pinscape) of the material. We use strong pinning theory to derive a microscopic expression for the Campbell length λ(C), the penetration depth of the ac signal. We show that λ(C) is determined by the jump in the pinning force, in contrast to the critical current j(c), which involves the jump in pinning energy. We demonstrate that the Campbell lengths generically differ for zero-field-cooled and field-cooled samples and predict that hysteretic behavior can appear in the latter situation. We compare our findings with new experimental data and show the potential of this technique in providing information on the material's pinscape.
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Quantum engineering requires controllable artificial systems with quantum coherence exceeding the device size and operation time. This can be achieved with geometrically confined low-dimensional electronic structures embedded within ultraclean materials, with prominent examples being artificial atoms (quantum dots) and quantum corrals (electronic cavities). Combining the two structures, we implement a mesoscopic coupled dot-cavity system in a high-mobility two-dimensional electron gas, and obtain an extended spin-singlet state in the regime of strong dot-cavity coupling. Engineering such extended quantum states presents a viable route for nonlocal spin coupling that is applicable for quantum information processing.
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In a coupled system of one classical and one quantum mechanical degree of freedom, the quantum degree of freedom can facilitate the escape of the whole system. Such unusual escape characteristics have been theoretically predicted as the "Münchhausen effect." We implement such a system by shunting one of the two junctions of a dc SQUID with an additional capacitance. In our experiments, we detect a crossover between quantum and classical escape processes related to the direction of escape. We find that, under varying external magnetic flux, macroscopic quantum tunneling periodically alternates with thermally activated escape, a hallmark of the "Münchhausen effect."
RESUMEN
We determine the current-voltage characteristic of type-II superconductors in the presence of strong pinning centers. Focusing on a small density of defects, we derive a generic form for the characteristic with a linear flux-flow branch shifted by the critical current (excess-current characteristic). The details near onset, a hysteretic jump (for κ>>1) or a smooth velocity turn-on (κâ1), depend on the Labusch parameter κ characterizing the pinning centers. Pushing the single-pin analysis into the weak pinning domain, we reproduce the collective pinning results for the critical current.
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We study a single-electron pulse injected into the chiral edge state of a quantum Hall device and subject it to a capacitive Coulomb interaction. We find that the scattered multiparticle state remains unentangled and hence can be created itself by a suitable classical voltage pulse. The application of an appropriate inverse pulse corrects for the shakeup due to the interaction and resurrects the original injected wave packet. We suggest an experiment with an asymmetric Mach-Zehnder interferometer where the application of such pulses manifests itself in an improved visibility.
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We present an analytic slave-boson approach to calculate the elementary excitations of the Jaynes-Cummings-Hubbard model (JCHM) describing strongly correlated polaritons on a lattice in various quantum optical systems. In the superfluid phase near the Mott transition we find a gapless, linear Goldstone mode and a gapped amplitude mode corresponding to phase and density fluctuations, respectively. The sound velocity of the Goldstone mode develops a peculiar anomaly as a function of detuning at low densities, which persists into the weakly interacting regime of a polariton BEC.
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We investigate the liquid-glass phase transition in a system of pointlike particles interacting via a finite-range attractive potential in D -dimensional space. The phase transition is driven by an "entropy crisis" where the available phase space volume collapses dramatically at the transition. We describe the general strategy underlying the first-principles replica calculation for this type of transition; its application to our model system then allows for an analytic description of the liquid-glass phase transition within a mean-field approximation, provided the parameters are chosen suitably. We find a transition exhibiting all the features associated with an entropy crisis, including the characteristic finite jump of the order parameter at the transition while the free energy and its first derivative remain continuous.
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We calculate the melting line of the pancake-vortex system in a layered superconductor, interpolating between two-dimensional (2D) melting at high fields and the zero-field limit of single-stack evaporation. Long-range interactions between pancake vortices in different layers permit a mean-field approach, the "substrate model, " where each 2D crystal fluctuates in a substrate potential due to the vortices in other layers. We find the thermal stability limit of the 3D solid, and compare the free energy to a 2D liquid to determine the first-order melting transition and its jump in entropy.
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One hundred and thirty-eight patients (142 shoulders) who had recurrent anterior instability of the shoulder that was unresponsive to a specific physician-directed rehabilitation program were managed with an anatomical capsular imbrication reconstruction. The procedure included repair of the capsulolabral injury, when present, and reinforcement of the anteroinferior capsular ligaments with an imbrication technique that decreases the over-all capsular volume. The shoulders were divided into two groups: 108 shoulders in which the recurrent instability was related to a defined traumatic episode (Group I) and thirty-four shoulders with no distinct history of trauma (Group II). The anatomical capsular imbrication was the primary procedure in ninety shoulders and was used to treat at least one failed previous reconstruction in fifty-two shoulders. According to the grading system of Rowe et al., 93 per cent (132) of the shoulders had a good or excellent result at an average of five years (range, two or twelve years) after the operation. The results after a previous failed reconstruction were especially encouraging. Of the fifty-two shoulders that had had at least one previous reconstructive procedure, forty had an excellent result, five had a good result, four had a fair result, and three had a poor result. The results of this study suggest that this procedure restores stability while preserving a functional range of motion in patients who have symptomatic recurrent anterior instability of the shoulders, regardless of the etiology.
Asunto(s)
Inestabilidad de la Articulación/cirugía , Articulación del Hombro , Adolescente , Adulto , Femenino , Humanos , Masculino , Persona de Mediana Edad , Ortopedia/métodos , Satisfacción del Paciente , Rango del Movimiento Articular , Recurrencia , Resultado del TratamientoRESUMEN
Expeditious and stereocontrolled syntheses are reported of beta-D-Glc pNAc-(1-->4)-[beta-D-Glc pA-(1-->3)-beta-D-Glc pNAc-(1-->4)]n-beta-D-Glc pA-(1-->OMe), where n = 1, 2, and 3, which represent structural elements of the extracellular polysaccharide hyaluronic acid. Condensation of 4,6-O-benzylidene-3-O-chloroacetyl-2-deoxy-2-trichloroacetamido- alpha-D-glucopyranosyl trichloroacetimidate with methyl (4-methoxyphenyl 2,3-di-O-benzoyl-beta-D-glucopyranosid)uronate gave the disaccharide derivative 9, which was demethoxyphenylated and imidoylated to afford the pivotal disaccharide trichloroacetimidate 7. Condensation of 7 with methanol followed by O-dechloroacetylation gave the acceptor 8. Coupling of 7 with 8 gave the tetrasaccharide derivative 4. O-Dechloroacetylation of 4 followed by condensation with imidate 7 afforded hexasaccharide 5, which was transformed into octasaccharide 6 by a similar two-step procedure. Subsequent O-dechloroacetylation, transformation of the N-trichloroacetyl groups into N-acetyl, debenzylidenation, and saponification of 4-6 afforded the tetra- (1), hexa- (2), and octa-saccharide (3) derivatives in high yields, as their sodium salts.
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Glucósidos/síntesis química , Glucuronatos/análisis , Ácido Hialurónico/análogos & derivados , Oligosacáridos/síntesis química , Conformación de Carbohidratos , Secuencia de Carbohidratos , Glucósidos/química , Espectroscopía de Resonancia Magnética , Datos de Secuencia Molecular , Oligosacáridos/químicaRESUMEN
3,4,6-Tri-O-acetyl-2-deoxy-2-trichloroacetamido-alpha-D-glucopyran osyl trichloroacetimidate and its O-benzylated analogue were tested as glycosyl donors in the reaction with a set of sugar acceptors unsubstituted on O-3 and O-4, typically encountered in the synthesis of oligosaccharides. Glycosides were obtained in good to excellent yields with only a slight excess (1.1-1.2 equiv) of the donor, and with a high degree of 1,2-trans stereoselectivity. The corresponding 2-(trichloromethyl)oxazolinium ion was postulated to be the major reactive intermediate. The N-trichloroacetyl groups in the disaccharide products were easily transformed into N-acetyl under neutral conditions by reduction with tributylstannane.
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Desoxiglucosa/análogos & derivados , Disacáridos/síntesis química , Oligosacáridos/síntesis química , Conformación de Carbohidratos , Secuencia de Carbohidratos , Disacáridos/química , Glicósidos/síntesis química , Indicadores y Reactivos , Espectroscopía de Resonancia Magnética , Datos de Secuencia Molecular , Oligosacáridos/química , Rotación Óptica , EstereoisomerismoRESUMEN
A 59-year-old woman with calcific tendinitis in her right shoulder underwent extracorporeal shock-wave lithotripsy. Three years and four months later she presented with osteonecrosis of the head of the right humerus. It is known that shock waves in patients with urological disorders can damage blood vessels. A possible reason for the development of osteonecrosis in this patient may have been damage to the blood supply of the head of the humerus.
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Ondas de Choque de Alta Energía/efectos adversos , Húmero , Osteonecrosis/etiología , Femenino , Ondas de Choque de Alta Energía/uso terapéutico , Humanos , Húmero/irrigación sanguínea , Persona de Mediana Edad , Articulación del Hombro , Tendinopatía/terapiaRESUMEN
Although the clinical experience with reamed intramedullary nailing has been successful for the treatment of femur and tibia fractures, similar success has not been duplicated when this technique has been applied in the humerus. Although the cortical vascular response to nailing of the humerus is presently assumed to be similar to that of the femur, the response of the humerus to reaming has not been documented in vivo. The following case depicts avascularity of the humeral diaphyseal cortex as a complication of reamed intramedullary nailing and illustrates the sensitivity of the humerus to this treatment.
Asunto(s)
Fijación Intramedular de Fracturas/efectos adversos , Fracturas del Húmero/cirugía , Húmero/irrigación sanguínea , Adulto , Femenino , Humanos , Fracturas del Húmero/patologíaRESUMEN
A sonographic method of measuring instability of the subtalar joint was developed. After defining reference points, we determined a sonographic fibulo-trochlear angle. This angle was measured in a neutral position and under an inversion stress position. A ratio q representing the relationship between the fibulo-trochlear angle measured in the neutral position and under stress, was determined. The method was tested on volunteers with clinically and radiologically stable subtalar joints and a control group with unstable subtalar joints. The stress radiograph using the Zwipp method was utilized for radiologic correlation. A sonographic ratio q>1.6 correlated with a radiological unstable subtalar joint. The borderline zone in which there was an overlap of stable and unstable subtalar joints was characterized by a q value of 1.2-1.6. A ratio q<1.2 correlated with a stable subtalar joint.
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Inestabilidad de la Articulación/diagnóstico por imagen , Rango del Movimiento Articular/fisiología , Articulación Talocalcánea/diagnóstico por imagen , Articulación Talocalcánea/fisiopatología , Cadáver , Femenino , Humanos , Masculino , Radiografía , Valores de Referencia , Sensibilidad y Especificidad , UltrasonografíaRESUMEN
The load axis of the curved-shaped proximal femur lies not inside, but outside the bone. Therefore high bending forces are acting, the medial cortex absorbing pressure, the lateral cortex absorbing tension. In a transverse fracture, a laterally applied plate will absorb the tensile stresses, the medial cortex the pressure forces. When medial butress due to bony defect is missing, the laterally applied plate is subjected to cycling bending and will undergo fatigue fracture. This dilemma is compensated by a wave-plate with bone graft: The compression forces are detoured to the lateral cortex and the plate is again subjected to tension. Furthermore since the plate is standing away from the bone, the plate does not disturb the blood supply at the fracture side and bone healing.
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Placas Óseas , Fracturas del Fémur/cirugía , Fijación Interna de Fracturas/métodos , Adulto , Fracturas del Fémur/diagnóstico por imagen , Fijación Interna de Fracturas/instrumentación , Humanos , Masculino , Radiografía , ReoperaciónRESUMEN
This study will present trends and recommendations to increase active and passive safety in paragliding on the basis of current state-of-the-art equipment and typical patterns of injury. This German-Swiss teamwork presents data of 55 male and 9 female patients treated after paragliding accidents between 1994 to 1998 respectively 1996 to 1998. 43.7% of the pilots presented with multiple injuries, 62.5% suffered spinal fractures and 18.8% pelvic fractures. 28.4% of the injured pilots were admitted with injuries of the lower extremities mainly affecting the tarsus or the ankle joint. Only three patients with single injuries could be treated in an ambulatory setting. 54.0% of the injuries left the patients with lasting functional residues and complaints. Main causes of accidents were either pilot error in handling the paraglider or general lack of awareness about potential risk factors. 46.0% of injuries occurred during landing, 42.9% of injuries during the flight and another 11.1% of injuries during starting procedures. With noticeable enhanced performance sails of the beginners and intermediate level are increasingly popular. Protective helmets and sturdy footwear reaching above the ankle joint are indispensable pieces of equipment. The use of protective gloves is highly recommended. Back protection devices of the new generation provide the best passive prophylaxis for the pilot against pelvic and spinal cord injuries. This area hold the most promise for increasing safety and reducing risk of injury in future, apart from using beginners and intermediate wings. After acquisition of the pilot license performance and security training provide the best preparing to master unforeseeable situations.
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Traumatismos en Atletas/epidemiología , Traumatismos en Atletas/prevención & control , Fracturas Óseas/epidemiología , Equipos de Seguridad , Equipo Deportivo , Deportes/estadística & datos numéricos , Prevención de Accidentes , Adolescente , Adulto , Traumatismos en Atletas/etiología , Femenino , Alemania/epidemiología , Humanos , Masculino , Persona de Mediana Edad , Ropa de Protección , Estudios Retrospectivos , Deportes/educación , Suiza/epidemiologíaRESUMEN
An osteotomy of the first row for the treatment of hallux valgus is indicated for younger patients with minor to moderate valgus deformation and only minor arthritic changes in the first metatarsophalangeal joint. The osteotomy has two prominent goals: Correction of the deformity and restoration of muscle function and muscular balance. Especially the later seems to be essential for preventing failures in the long term. Osteotomies can be carried out on os cuneiforme mediale, metatarsal bone (proximal, shaft, subcapital) and phalanx. The cuneiforme osteotomy isn't recommended because of alterations in the joint between the medial and intermedium cuneiforme. Osteotomies of the proximal metatarsal bone are rarely performed and mostly combined with an arthroplastic procedure of the metatarsophalangeal joint. The disadvantage of a shaft osteotomy (Ludloff's osteotomy) is the long time for healing of the osteotomy of diaphysis of the metatarsal bone. Subcapital osteotomies are most frequently performed. With a subcapital osteotomy you can correct more deformities than with the other osteotomies. The phalangeal osteotomy is indicated just in special cases. The combination of a subcapital and a phalangeal osteotomy is recommended by Magerl in order to reduce the failure rates.