Lasing in Single Cadmium Sulfide Nanowire Optical Cavities

The mechanism of lasing in single cadmium sulfide (CdS) nanowire cavities was elucidated by temperature-dependent and time-resolved photoluminescence (PL) measurements. Temperature-dependent PL studies reveal rich spectral features and show that an exciton-exciton interaction is critical to lasing up to 75 K, while an exciton-phonon process dominates at higher temperatures. These measurements together with temperature and intensity dependent life-time and threshold studies suggest that lasing is due to formation of excitons, and moreover, have implications for the design of efficient, low-threshold nanowire lasers.Comment: 4 figure

Transatlantic Politics After the 2008 Election

The fundamental realities on which the Atlantic relationship rests remain in place and are highly unlikely to disappear at any time in the foreseeable future. Whoever the American voters choose in the 2008 presidential election, Europe is likely to experience a political honeymoon with the new President and feel relieved at the departure of the Bush Administration. However, it is important to avoid the misconception that has all too frequently distorted discussion of this subject during the past eight years: that the largely harmonious relations between the US and its European partners were rudely interrupted by the coming to power of the Bush Administration with what are said to be its unilateral, aggressive and warlike habits. Issues such as Iran, the Middle East, terrorism and international trade will ensure that there will not be the kind of easy harmony and seamless multilateralism that some observers have explicitly or implicitly ascribed to the pre-George W. Bush years and assumed would re-emerge in the post-Bush era. On the other hand, the fundamental realities on which the Atlantic relationship rests remain in place and are highly unlikely to disappear at any time in the foreseeable future

La política exterior en las elecciones presidenciales de EEUU después del “Super Martes”

Tras reducirse el número de candidatos después del “Super Martes”, los observadores podrán centrar más su atención a partir de ahora en lo que una presidencia de McCain, Clinton u Obama supondría en política exterior. Después de casi un año de campaña política, las esperadísimas primarias del “Super Martes” han clarificado finalmente la competición por la elección presidencial. Las elecciones generales propiamente dichas no tendrán lugar hasta el 6 de noviembre, dentro de casi nueve meses, pero ya es seguro que el candidato republicano será el senador John McCain, y el candidato demócrata será o bien Hillary Rodham Clinton o Barak Obama. Al reducirse el número de candidatos, los observadores dentro y fuera de EEUU podrán prestar mayor atención a lo que significará la presidencia de McCain, Clinton u Obama en términos de política y especialmente en asuntos exteriores

National trends in total hip arthroplasty for traumatic hip fractures: An analysis of a nationwide all-payer database.

BACKGROUND: Hemiarthroplasty (HA) has traditionally been the treatment of choice for elderly patients with displaced femoral neck fractures. Ideal treatment for younger, ambulatory patients is not as clear. Total hip arthroplasty (THA) has been increasingly utilized in this population however the factors associated with undergoing HA or THA have not been fully elucidated. AIM: To examine what patient characteristics are associated with undergoing THA or HA. To determine if outcomes differ between the groups. METHODS: We queried the Nationwide Inpatient Sample (NIS) for patients that underwent HA or THA for a femoral neck fracture between 2005 and 2014. The NIS comprises a large representative sample of inpatient hospitalizations in the United States. International Classifications of Disease, Ninth Edition (ICD-9) codes were used to identify patients in our sample. Demographic variables, hospital characteristics, payer status, medical comorbidities and mortality rates were compared between the two procedures. Multivariate logistic regression analysis was then performed to identify independent risk factors of treatment utilized. RESULTS: Of the total 502060 patients who were treated for femoral neck fracture, 51568 (10.3%) underwent THA and the incidence of THA rose from 8.3% to 13.7%. Private insurance accounted for a higher percentage of THA than hemiarthroplasty. THA increased most in urban teaching hospitals relative to urban non-teaching hospitals. Mean length of stay (LOS) was longer for HA. The mean charges were less for HA, however charges decreased steadily for both groups. HA had a higher mortality rate, however, after adjusting for age and comorbidities HA was not an independent risk factor for mortality. Interestingly, private insurance was an independent predictor for treatment with THA. CONLUSION: There has been an increase in the use of THA for the treatment of femoral neck fractures in the United States, most notably in urban hospitals. HA and THA are decreasing in total charges and LOS

Magnetoconductance oscillations in quasiballistic multimode nanowires

We calculate the conductance of quasi-one-dimensional nanowires with electronic states confined to a surface charge layer, in the presence of a uniform magnetic field. Two-terminal magnetoconductance (MC) between two leads deposited on the nanowire via tunnel barriers is dominated by density-of-states (DOS) singularities, when the leads are well apart. There is also a mesoscopic correction due to a higher-order coherent tunneling between the leads for small lead separation. The corresponding MC structure depends on the interference between electron propagation via different channels connecting the leads, which in the simplest case, for the magnetic field along the wire axis, can be crudely characterized by relative winding numbers of paths enclosing the magnetic flux. In general, the MC oscillations are aperiodic, due to the Zeeman splitting, field misalignment with the wire axis, and a finite extent of electron distribution across the wire cross section, and are affected by spin-orbit coupling. The quantum-interference MC traces contain a wealth of information about the electronic structure of multichannel wires, which would be complimentary to the DOS measurements. We propose a four-terminal configuration to enhance the relative contribution of the higher-order tunneling processes and apply our results to realistic InAs nanowires carrying several quantum channels in the surface charge-accumulation layer.Comment: 11 pages, 8 figure

Bost-Connes systems and F1F_1-structures in Grothendieck rings, spectra, and Nori motives

We construct geometric lifts of the Bost-Connes algebra to Grothendieck rings and to the associated assembler categories and spectra, as well as to certain categories of Nori motives. These categorifications are related to the integral Bost-Connes algebra via suitable Euler characteristic type maps and zeta functions, and in the motivic case via fiber functors. We also discuss aspects of F1-geometry, in the framework of torifications, that fit into this general setting

Hole Spin Coherence in a Ge/Si Heterostructure Nanowire

Relaxation and dephasing of hole spins are measured in a gate-defined Ge/Si nanowire double quantum dot using a fast pulsed-gate method and dispersive readout. An inhomogeneous dephasing time $T_2^* \sim 0.18~\mathrm{\mu s}$ exceeds corresponding measurements in III-V semiconductors by more than an order of magnitude, as expected for predominately nuclear-spin-free materials. Dephasing is observed to be exponential in time, indicating the presence of a broadband noise source, rather than Gaussian, previously seen in systems with nuclear-spin-dominated dephasing.Comment: 15 pages, 4 figure

Antilocalization of Coulomb Blockade in a Ge-Si Nanowire

The distribution of Coulomb blockade peak heights as a function of magnetic field is investigated experimentally in a Ge-Si nanowire quantum dot. Strong spin-orbit coupling in this hole-gas system leads to antilocalization of Coulomb blockade peaks, consistent with theory. In particular, the peak height distribution has its maximum away from zero at zero magnetic field, with an average that decreases with increasing field. Magnetoconductance in the open-wire regime places a bound on the spin-orbit length ($l_{so}$ < 20 nm), consistent with values extracted in the Coulomb blockade regime ($l_{so}$ < 25 nm).Comment: Supplementary Information available at http://bit.ly/19pMpd

Gate Coupling to Nanoscale Electronics

The realization of single-molecule electronic devices, in which a nanometer-scale molecule is connected to macroscopic leads, requires the reproducible production of highly ordered nanoscale gaps in which a molecule of interest is electrostatically coupled to nearby gate electrodes. Understanding how the molecule-gate coupling depends on key parameters is crucial for the development of high-performance devices. Here we directly address this, presenting two- and three-dimensional finite-element electrostatic simulations of the electrode geometries formed using emerging fabrication techniques. We quantify the gate coupling intrinsic to these devices, exploring the roles of parameters believed to be relevant to such devices. These include the thickness and nature of the dielectric used, and the gate screening due to different device geometries. On the single-molecule (~1nm) scale, we find that device geometry plays a greater role in the gate coupling than the dielectric constant or the thickness of the insulator. Compared to the typical uniform nanogap electrode geometry envisioned, we find that non-uniform tapered electrodes yield a significant three orders of magnitude improvement in gate coupling. We also find that in the tapered geometry the polarizability of a molecular channel works to enhance the gate coupling