Tuning Electroluminescence from a Plasmonic Cavity-Coupled Silicon Light Source.

The combination of Moore's law and Dennard's scaling rules have constituted the fundamental guidelines for the silicon-based semiconductor industry for decades. Furthermore, the enormous growth of global data volume has pushed the demand for complex and densely packed devices. In recent years, it has become clear that wired interconnects impose increasingly severe speed and power limitations onto integrated circuits as scaling slows toward a halt. To overcome these limitations, there is a clear need for optical data processing. Despite significant progress in the development of silicon photonics, light sources remain challenging owing to the indirect bandgap of group IV materials. It is therefore highly desirable to develop new concepts for a silicon light source that meets efficiency and footprint requirements similar to their electronic counterparts. Here, we demonstrate an electrically driven and tunable silicon light source by matching the resonant modes of a silver nanocavity with the hot luminescence spectrum of an avalanching p-n junction. The cavity significantly enhances phonon-assisted recombination of hot carriers by tailoring the local density of states at the size-tunable resonance. Such tunable nanoscale emitter may be of great interest for short-reach communications, microdisplays or lab-on-chip applications.

A precision flow-controlled Rb-82 generator for bolus or constant-infusion studies of the heart and brain.

A precision flow-controlled rubidium-82 generator has been constructed to deliver 76-sec Rb-82 at either fast or slow flow rates for bolus or constant-infusion studies. A stepping motor drive is interfaced to a microprocessor for pulsed control of flow rate to deliver the saline eluant solution from a large-volume (150 ml) machined pumping syringe through an alumina column that retains the 25-day Sr-82 parent. The generator system delivers 70-90% of the maximum Rb-82 activity in a 20-25 ml bolus elution of 2% NaCl. The Sr-82/Sr-85 breakthrough is 10(-7) - 10(-6). both yield and breakthrough are functions of column length and flow rate. Six separate Sr-82 loadings of the generator were evaluated over a period of nearly 2 yr in studies of myocardial blood perfusion and permeability changes in the blood-brain barrier. Sterility and apyrogenicity of the Rb-82 eluate were maintained during multiple elutions and long-term use of 3-4 mo for each generator loading.

Amalgam margin breakdown caused by creep fatigue rupture.

This study was designed to determine whether the mechanical cyclic stressing that occurs during normal mastication contributes to margin breakdown of dental amalgam restorations. The method used appears to duplicate the mechanical stresses developed in vivo during mastication, as the result of tooth flexing. We evaluated one low-copper alloy--NTD--and three high-copper alloys--Dispersalloy, Phasealloy, and Tytin. We prepared simple amalgam restorations in a cavity centrally located in an aluminum beam. Each specimen received five periods of three-point cyclical loading (1.7 hertz, 4200 cycles at 37 degrees C). The margin area was subjected to SEM examination prior to and at the completion of each period of cycling. At the beginning of each period of cycling, beam deflection was set to establish a maximum theoretical stress of 1, 2, 4, 6, or 8 MPa. For all brands, cycling resulted in margin gap formation and surface wrinkling. Wrinkling in Dispersalloy occurred as a wide band of shallow wrinkles, whereas that in NTD occurred as a narrow band of deep wrinkles. At 21,000 cycles, very little void formation and fracturing had occurred in the Dispersalloy or NTD restorations. In contrast, the Phasealloy and Tytin restorations developed extensive fracturing even after 4200 cycles. Fracture surface analyses of Phasealloy and Tytin indicated that creep fatigue rupture was the fracture mechanism responsible for margin breakdown in these amalgam restorations, when subjected to cyclic compressive loading similar to that experienced during mastication.

Parity-violating electron scattering from 4He and the strange electric form factor of the nucleon.

We have measured the parity-violating electroweak asymmetry in the elastic scattering of polarized electrons from 4He at an average scattering angle = 5.7 degrees and a four-momentum transfer Q2 = 0.091 GeV2 . From these data, for the first time, the strange electric form factor of the nucleon G(E)s can be isolated. The measured asymmetry of A(PV) = (6.72 +/- 0.84(stat) +/- 0.21(syst) x 10(-6) yields a value of G(E)s = -0.038 +/- 0.042(stat) +/- 0.010(syst), consistent with zero.

Precision measurement of the weak mixing angle in Møller scattering.

We report on a precision measurement of the parity-violating asymmetry in fixed target electron-electron (Møller) scattering: A(PV) = [-131 +/- 14(stat) +/- 10(syst)] x 10(-9), leading to the determination of the weak mixing angle sin2(thetaW(eff) = 0.2397 +/- 0.0010(stat) +/- 0.0008(syst), evaluated at Q2 = 0.026 GeV2. Combining this result with the measurements of sin2(thetaW(eff) at the Z0 pole, the running of the weak mixing angle is observed with over 6sigma significance. The measurement sets constraints on new physics effects at the TeV scale.

Evaluation of a precipitation hardened wrought cobalt-nickel-chromium-titanium alloy for surgical implants.

A Co-Ni-Cr-Ti precipitation hardening alloy is evaluated for use as a surgical implant alloy. Static and fatigue strength studies indicate that the alloy is equivalent, or superior to, present implant alloys. In vitro and in vivo corrosion studies indicate that the material has good general corrosion resistance but may be susceptible to crevice corrosion. However, there appear to be no inherent difficulties in using precipitation hardened alloys for surgical implants and therefore it may be possible to develop a new class of materials possessing ultra-high strength and excellent corrosion resistance for use in surgical implant applications.

Electrochemical behavior of some commercial dental amalgams in artificial saliva.

Cathodic, linear anodic, and anodic polarization studies conducted on three commercial dental amalgams, Caulk Fine Cut Alloy, Spheralloy, and Dispersalloy, showed that all amalgams were in a passive state at the corrosion potential in synthetic saliva solution. The corrosion currents at the corrosion potential were therefore small for all the amalgams, in the range 0.08 to 0.30 muA/cm2. However, the Caulk Fine Cut Alloy and Spheralloy amalgams exhibited a breakdown of passivity and high anodic currents at potentials only approximately equal to 100 mV more noble than the corrosion potential whereas Dispersalloy amalgams maintained passivity at potentials up to 700 mV more noble than the corrosion potential. The breakdown of passivity in Caulk Alloy and Spheralloy amalgams is attributed to the presence of the gamma2 phase (Sn7-8Hg) whereas the passive behavior of Dispersalloy amalgam is attributed to the absence of the phase. It is concluded that none of the amalgams will exhibit severe general corrosion in use, but that both Caulk Alloy and Spheralloy amalgams will exhibit pitting corrosion whereas this type of corrosion should be minimal in Dispersalloy amalgams.

Corrosion fatigue of surgical stainless steel in synthetic physiological solution.

Fatigue tests conducted both in air and synthetic physiological solution show that the fatigue strength of surgical stainless steel in synthetic physiological solution is about 10% lower than the strength in air for a given endurance level. It is proposed that surgical stainless steel which is normally passive in physiological solution suffers corrosion fatigue because of susceptibility to crevice corrosion which occurs at extrusions and intrusions (crevices) on the surface thereby shortening the crack initiation time and the fatigue life.

The concept of protection potential applied to the corrosion of metallic orthopedic implants.

Cyclic polarization curves obtained for a cobalt-base casting alloy (similar to Vitallium Surgical Alloy) and for 316L stainless steel show that the cobalt-base alloy exhibits a high (noble) protection potential whereas the stainless steel exhibits a low (active) protection potential. It is suggested that the resistance to crevice corrosion of Vitallium Surgical Alloy results from its high value of protection potential whereas the susceptibility of 316L stainless to severe crevice corrosion results from its low value of protection potential.

Preparation of 11C-methyl iodide and L-[S-methyl-11C]methionine by an automated continuous flow process.

A continuous flow procedure has been developed for the synthesis of 11C-methyl iodide and L-[S-methyl-11C]methionine from 11CO2. The preparation can be completed in 20 min after the end of bombardment. This procedure results in the production of approximately 44 mCi 11C-methyl methionine with a specific activity of 3.3 Ci/mmol. Radiochemical purity is greater than 96%. The procedure has been automated so that the preparation can be carried out remotely, thus minimizing exposure of personnel to radiation.

Three dimensional imaging of the myocardium with radionuclides.

Transverse sections of the distribution of 129Cs and 201Ti in the human myocardium were obtained using 36 and 72 views of the thorax with a large field of view Anger camera. The cardiac cycle was divided into 100-msec intervals to obtain motion images of an average cycle of the beating heart. At least 300,000 events must be detected for each cardiac phase of each section for quantitative work. Over 8 million events from the upper thorax must be accumulated in gated studies if three or more sections are obtained for 8 intervals of 100 msec to 150 msec.