Multiband Mechanism for the Sign Reversal of Coulomb Drag Observed in Double Bilayer Graphene Heterostructures.

Coupled 2D sheets of electrons and holes are predicted to support novel quantum phases. Two experiments of Coulomb drag in electron-hole (e-h) double bilayer graphene (DBLG) have reported an unexplained and puzzling sign reversal of the drag signal. However, we show that this effect is due to the multiband character of DBLG. Our multiband Fermi liquid theory produces excellent agreement and captures the key features of the experimental drag resistance for all temperatures. This demonstrates the importance of multiband effects in DBLG: they have a strong effect not only on superfluidity, but also on the drag.

Inhomogeneous phases in coupled electron-hole bilayer graphene sheets: Charge Density Waves and Coupled Wigner Crystals.

Recently proposed accurate correlation energies are used to determine the phase diagram of strongly coupled electron-hole graphene bilayers. The control parameters of the phase diagram are the charge carrier density and the insulating barrier thickness separating the bilayers. In addition to the electron-hole superfluid phase we find two new inhomogeneous ground states, a one dimensional charge density wave phase and a coupled electron-hole Wigner crystal. The elementary crystal structure of bilayer graphene plays no role in generating these new quantum phases, which are completely determined by the electrons and holes interacting through the Coulomb interaction. The experimental parameters for the new phases lie within attainable ranges and therefore coupled electron-hole bilayer graphene presents itself as an experimental system where novel emergent many-body phases can be realized.

Multicomponent Electron-Hole Superfluidity and the BCS-BEC Crossover in Double Bilayer Graphene.

Superfluidity in coupled electron-hole sheets of bilayer graphene is predicted here to be multicomponent because of the conduction and valence bands. We investigate the superfluid crossover properties as functions of the tunable carrier densities and the tunable energy band gap E_{g}. For small band gaps there is a significant boost in the two superfluid gaps, but the interaction-driven excitations from the valence to the conduction band can weaken the superfluidity, even blocking the system from entering the Bose-Einstein condensate (BEC) regime at low densities. At a given larger density, a band gap E_{g}∼80-120 meV can carry the system into the strong-pairing multiband BCS-BEC crossover regime, the optimal range for realization of high-T_{c} superfluidity.

Effect of carrier tunneling on the structure of Si nanowires fabricated by metal assisted etching.

The metal assisted etching mechanism for Si nanowire fabrication, triggered by doping type and level and coupled with choice of metal catalyst, is still very poorly understood. We explain the different etching rates and porosities of wires we observe based on extensive experimental data, using a new empirical model we have developed. We establish as a key parameter, the tunneling through the space charge region (SCR) which is the result of the reduction of the SCR width by level of the Si wafer doping in the presence of the opposite biases of the p- and n-type wafers. This improved understanding should permit the fabrication of high quality wires with predesigned structural characteristics, which hitherto has not been possible.

Large gap electron-hole superfluidity and shape resonances in coupled graphene nanoribbons.

We predict enhanced electron-hole superfluidity in two coupled electron-hole armchair-edge terminated graphene nanoribbons separated by a thin insulating barrier. In contrast to graphene monolayers, the multiple subbands of the nanoribbons are parabolic at low energy with a gap between the conduction and valence bands, and with lifted valley degeneracy. These properties make screening of the electron-hole interaction much weaker than for coupled electron-hole monolayers, thus boosting the pairing strength and enhancing the superfluid properties. The pairing strength is further boosted by the quasi one-dimensional quantum confinement of the carriers, as well as by the large density of states near the bottom of each subband. The latter magnifies superfluid shape resonances caused by the quantum confinement. Several superfluid partial condensates are present for finite-width nanoribbons with multiple subbands. We find that superfluidity is predominately in the strongly-coupled BEC and BCS-BEC crossover regimes, with large superfluid gaps up to 100 meV and beyond. When the gaps exceed the subband spacing, there is significant mixing of the subbands, a rounding of the shape resonances, and a resulting reduction in the one-dimensional nature of the system.

Enhancement of electron-hole superfluidity in double few-layer graphene.

We propose two coupled electron-hole sheets of few-layer graphene as a new nanostructure to observe superfluidity at enhanced densities and enhanced transition temperatures. For ABC stacked few-layer graphene we show that the strongly correlated electron-hole pairing regime is readily accessible experimentally using current technologies. We find for double trilayer and quadlayer graphene sheets spatially separated by a nano-thick hexagonal boron-nitride insulating barrier, that the transition temperature for electron-hole superfluidity can approach temperatures of 40 K.

High-temperature superfluidity in double-bilayer graphene.

Exciton bound states in solids between electrons and holes are predicted to form a superfluid at high temperatures. We show that by employing atomically thin crystals such as a pair of adjacent bilayer graphene sheets, equilibrium superfluidity of electron-hole pairs should be achievable for the first time. The transition temperatures are well above liquid helium temperatures. Because the sample parameters needed for the device have already been attained in similar graphene devices, our work suggests a new route toward realizing high-temperature superfluidity in existing quality graphene samples.

Segmentation of epithelium in H&E stained odontogenic cysts.

An algorithm for the automated segmentation of epithelial tissue in digital images of histologic tissue sections of odontogenic cysts (cysts originating from residual odontogenic epithelium) is presented. The algorithm features an image standardization process that greatly reduces variation in luminance and chrominance between images due to variations in sample preparation. Segmentation of the epithelial regions of images uses an algorithm based on binary graph cuts where graph weights depend on probabilities obtained from colour histogram models of epithelium and stroma image regions. Algorithm training used a data set of 38 images of four types of odontogenic cyst and was tested using a separate data set of 35 images of the same four cyst types. The best parameters for the segmentation algorithm were determined using a response-surface optimizer. The best parameter set resulted in an overall mean (± std. dev.) sensitivity of 91.5 ± 17% and overall mean specificity of 85.1 ± 18.6% on the training set. Particularly good results were obtained for dentigerous and odontogenic keratocysts for which the mean sensitivities/specificities were 91.9 ± 6.15%/97.4 ± 2.15% and 96.1 ± 1.98%/98.7 ± 3.16%, respectively. Our method is potentially applicable to many pathological conditions in similar tissues, such as skin and mucous membranes where there is a clear microscopic distinction between epithelium and connective tissues.

[Infection-triggered familial or recurrent acute necrotizing encephalopathy]. / Encefalopatía aguda necrosante familiar o recurrente desencadenada por infecciones.

Acute necrotizing encephalopathy (ANE) presents in children after common viral infections. Most cases of ANE are non-familial and non-recurrent and have been mainly reported in Asian patients, although ANE affects children worldwide. Recently, missense mutations in the gene encoding the nuclear pore protein Ran Binding Protein 2 (RANBP2) have been found in several families with familial or recurrent cases of ANE. We describe a Spanish family with familial and recurrent ANE without mutations in RANBP2. Mutations in RANBP2 are not the sole susceptibility alleles for familial or recurrent ANE.

Extending uses of holmium:yttrium-aluminum-garnet laser--deflating blocked catheter balloon.

The nondeflating catheter balloon is infrequently encountered by urologists and can pose quite a challenge. We describe a new technique for its removal using the holmium:yttrium-aluminum-garnet laser when noninvasive methods have failed.

Autosomal dominant acute necrotizing encephalopathy.

OBJECTIVE: To define the clinical and biochemical abnormalities of an autosomal dominant form of acute encephalopathy. METHODS: The clinical details of 11 affected family members in comparison with 63 unaffected relatives were analyzed. RESULTS: Affected children become comatose after onset of a febrile illness. Outcomes include full recovery, permanent neurologic impairment, and death. Recurrences produce more severe impairments. Lesions of necrotizing encephalopathy of the thalamus and brainstem are present on autopsy and MRI. Oxidative phosphorylation of intact mitochondria from a muscle biopsy shows loose coupling. Unaffected family members, including obligate carriers, share no clinical characteristics, demonstrating incomplete penetrance. CONCLUSIONS: Characteristic pathology and MRI findings define this disorder of autosomal dominant acute encephalopathy. Leigh syndrome and sporadic acute necrotizing encephalopathy share similarities but are distinct.

Local anaesthetic for transrectal ultrasound-guided prostate biopsy: a prospective, randomized, double blind, placebo-controlled study.

OBJECTIVE: To evaluate the efficacy of local anaesthetic (LA) infiltration in decreasing the discomfort experienced by patients undergoing transrectal ultrasound (TRUS)-guided biopsy of prostate. PATIENTS AND METHODS: 98 patients were randomized to receive 3x3ml of 1% lidocaine (n=55) or saline (n=43). The injection sites were basolaterally on each side to infiltrate the neuro-vascular bundle and one at the apex. Generally 12 systematic random biopsies were performed after which patients were asked to grade the pain of the whole procedure using a visual analogue scale ranging from 0 to 10. RESULTS: The LA group had a significantly lower pain score compared with placebo. The mean pain scores were 3.0 and 4.3 (p<0.001), respectively. Using an unpaired t-test, the difference between means was -1.96 to -0.51 with 95% confidence interval. There were no significant problems associated with the infiltration of either saline or LA. CONCLUSION: Local anaesthesia for TRUS biopsy is simple and well tolerated. It significantly reduces the pain associated with the procedure. We recommend its usage as a part of standard TRUS biopsy of the prostate.

Tolerance of optical interconnections to misalignment.

The fundamental reasons that determine the tolerance of free-space optical interconnect systems to misalignment are considered. By evaluation of the overlap of single-mode optical beams in the presence of misalignment it possible to determine an optimum beam configuration. It is shown that for any level of misalignment there is an optimum beam diameter that maximizes the coupling of light through the system. Many interconnect systems are not single mode throughout, so the analysis is extended to cover multimode systems. It is shown that, in principle, any level of misalignment can be accommodated by use of multimode beams, although at the cost of reduced channel density. It is shown that the presence of misalignment will mean that the number of channels that can be supported by an interconnect reduces with the length of the interconnect. As possible candidates for passively aligned systems, three example optical systems are analyzed by use of the methods developed.

Free-space optical relay for the interconnection of multimode fibers.

We present results from a system that shows that multimode fibers can be used for both the input and the output of a free-space optical system. The system consists of plastic microlenses integrated with plastic optomechanical components that are suitable for low-cost fabrication and assembly. Such a system opens up opportunities to construct large repeaters and switches for multigigabit ethernet applications by integration with two-dimensional arrays of optoelectronic devices. We demonstrate a 2.5-Gbit/s transmission rate by using commercial vertical-cavity surface-emitting lasers coupled to 62.5-microm core fibers. We consider the design constraints and the capabilities of custom optical modules suitable for mass production.

Optoelectronic Systems Based on InGaAs- Complementary-Metal-Oxide-Semiconductor Smart-Pixel Arrays and Free-Space Optical Interconnects.

Free-space optical interconnects have been identified as a potentially important technology for future massively parallel-computing systems. The development of optoelectronic smart pixels based on InGaAs/AlGaAs multiple-quantum-well modulators and detectors flip-chip solder-bump bonded onto complementary-metal-oxide-semiconductor (CMOS) circuits and the design and construction of an experimental processor in which the devices are linked by free-space optical interconnects are described. For demonstrating the capabilities of the technology, a parallel data-sorting system has been identified as an effective demonstrator. By use of Batcher's bitonic sorting algorithm and exploitation of a perfect-shuffle optical interconnection, the system has the potential to perform a full sort on 1024, 16-bit words in less than 16 mus. We describe the design, testing, and characterization of the smart-pixel devices and free-space optical components. InGaAs-CMOS smart-pixel, chip-to-chip communication has been demonstrated at 50 Mbits/s. It is shown that the initial system specifications can be met by the component technologies.