Application of the Density Matrix Renormalization Group in momentum space

We investigate the application of the Density Matrix Renormalization Group (DMRG) to the Hubbard model in momentum-space. We treat the one-dimensional models with dispersion relations corresponding to nearest-neighbor hopping and $1/r$ hopping and the two-dimensional model with isotropic nearest-neighbor hopping. By comparing with the exact solutions for both one-dimensional models and with exact diagonalization in two dimensions, we first investigate the convergence of the ground-state energy. We find variational convergence of the energy with the number of states kept for all models and parameter sets. In contrast to the real-space algorithm, the accuracy becomes rapidly worse with increasing interaction and is not significantly better at half filling. We compare the results for different dispersion relations at fixed interaction strength over bandwidth and find that extending the range of the hopping in one dimension has little effect, but that changing the dimensionality from one to two leads to lower accuracy at weak to moderate interaction strength. In the one-dimensional models at half-filling, we also investigate the behavior of the single-particle gap, the dispersion of spinon excitations, and the momentum distribution function. For the single-particle gap, we find that proper extrapolation in the number of states kept is important. For the spinon dispersion, we find that good agreement with the exact forms can be achieved at weak coupling if the large momentum-dependent finite-size effects are taken into account for nearest-neighbor hopping. For the momentum distribution, we compare with various weak-coupling and strong-coupling approximations and discuss the importance of finite-size effects as well as the accuracy of the DMRG.Comment: 15 pages, 11 eps figures, revtex

An InGaAlAs-InGaAs two-color photodetector for ratio thermometry

We report the evaluation of a molecular-beam epitaxy grown two-color photodetector for radiation thermometry. This two-color photodetector consists of two p+in+ diodes, an In0.53Ga0.25Al0.22As (hereafter InGaAlAs) p+in+ diode, which has a cutoff wavelength of 1180 nm, and an In0.53Ga0.47As (hereafter InGaAs) p+in+ diode with a cutoff wavelength of 1700 nm. Our simple monolithic integrated two-color photodetector achieved comparable output signal and signal-to-noise (SNR) ratio to that of a commercial two-color Si-InGaAs photodetector. The InGaAlAs and InGaAs diodes detect blackbody temperature as low as 275°C and 125°C, respectively, with an SNR above 10. The temperature errors extracted from our data are 4°C at 275°C for the InGaAlAs diode and 2.3°C at 125°C for the InGaAs diode. As a ratio thermometer, our two-color photodetector achieves a temperature error of 12.8°C at 275°C, but this improves with temperature to 0.1°C at 450°C. These results demonstrated the potential of InGaAlAs-InGaAs two-color photodetector for the development of high performance two-color array detectors for radiation thermometry and thermal imaging of hot objects

Ultraviolet Imaging with Low Cost Smartphone Sensors: Development and Application of a Raspberry Pi-Based UV Camera

Here, we report, for what we believe to be the first time, on the modification of a low cost sensor, designed for the smartphone camera market, to develop an ultraviolet (UV) camera system. This was achieved via adaptation of Raspberry Pi cameras, which are based on back-illuminated complementary metal-oxide semiconductor (CMOS) sensors, and we demonstrated the utility of these devices for applications at wavelengths as low as 310 nm, by remotely sensing power station smokestack emissions in this spectral region. Given the very low cost of these units, ≈ USD 25, they are suitable for widespread proliferation in a variety of UV imaging applications, e.g., in atmospheric science, volcanology, forensics and surface smoothness measurements

The impact of parent-created motivational climate on adolescent athletes' perceptions of physical self-concept

This is a preliminary version of this article. The official published version can be obtained from the link below.Grounded in expectancy-value model (Eccles, 1993) and achievement goal theory (Nicholls, 1989), this study examined the perceived parental climate and its impact on athletes' perceptions of competence and ability. Hierarchical regression analyses with a sample of 237 British adolescent athletes revealed that mothers and fathers' task- and ego-involving climate predicted their son's physical self-concept; the father in particular is the strongest influence in shaping a son's physical self-concept positively and negatively. It was also found that the self-concept of the young adolescent athlete is more strongly affected by the perceived parental-created motivational climate (both task and ego) than the older adolescent athlete's self-concept. These findings support the expectancy-value model assumptions related to the role of parents as important socializing agents, the existence of gender-stereotyping, and the heavy reliance younger children place on parents' feedback

High-Gain InAs Planar Avalanche Photodiodes

We report the fabrication of InAs planar avalanche photodiodes (APDs) using Be ion implantation. The planar APDs have a low background doping of $2 times 10^{14} {rm cm}^{-3}$ and large depletion widths approaching 8 μm. The thick depletion width enabled a gain of 330 to be achieved at −26 V at 200 K without inducing a significant tunneling current. No edge breakdown was observed within the APDs. The surface leakage current was found to be low with a gain normalized dark current density of 400 μAcm−2 at −20 V at 200 K

Distributed Management of Massive Data: an Efficient Fine-Grain Data Access Scheme

This paper addresses the problem of efficiently storing and accessing massive data blocks in a large-scale distributed environment, while providing efficient fine-grain access to data subsets. This issue is crucial in the context of applications in the field of databases, data mining and multimedia. We propose a data sharing service based on distributed, RAM-based storage of data, while leveraging a DHT-based, natively parallel metadata management scheme. As opposed to the most commonly used grid storage infrastructures that provide mechanisms for explicit data localization and transfer, we provide a transparent access model, where data are accessed through global identifiers. Our proposal has been validated through a prototype implementation whose preliminary evaluation provides promising results

InAs Diodes Fabricated Using Be Ion Implantation

Be ion implantation and annealing conditions were optimized to demonstrate an effective method for selective area p-type doping in InAs. Optimized implantation and annealing conditions were subsequently utilized to produce planar InAs diodes. The Be implanted planar diodes had a superior dynamic resistance-area product and comparable dark current with n-i-p InAs mesa diodes when operated at low temperatures

Building Capacity in a Rural North Carolina Community to Address Prostate Health Using a Lay Health Advisor Model

Background. Prostate cancer is a critical concern for African Americans in North Carolina (NC), and innovative strategies are needed to help rural African American men maximize their prostate health. Engaging the community in research affords opportunities to build capacity for teaching and raising awareness. Approach and Strategies. A community steering committee of academicians, community partners, religious leaders, and other stakeholders modified a curriculum on prostate health and screening to include interactive knowledge- and skill-building activities. This curriculum was then used to train 15 African American lay health advisors, dubbed Prostate Cancer Ambassadors, in a rural NC community. Over the 2-day training, Ambassadors achieved statistically significant improvements in knowledge of prostate health and maintained confidence in teaching. The Ambassadors, in turn, used their personal networks to share their knowledge with over 1,000 individuals in their community. Finally, the Ambassadors became researchers, implementing a prostate health survey in local churches. Discussion and Conclusions. It is feasible to use community engagement models for raising awareness of prostate health in NC African American communities. Mobilizing community coalitions to develop curricula ensures that the curricula meet the communities’ needs, and training lay health advisors to deliver curricula helps secure community buy-in for the information

Alignment of galaxy spins in the vicinity of voids

We provide limits on the alignment of galaxy orientations with the direction to the void center for galaxies lying near the edges of voids. We locate spherical voids in volume limited samples of galaxies from the Sloan Digital Sky Survey using the HB inspired void finder and investigate the orientation of (color selected) spiral galaxies that are nearly edge-on or face-on. In contrast with previous literature, we find no statistical evidence for departure from random orientations. Expressed in terms of the parameter c, introduced by Lee & Pen to describe the strength of such an alignment, we find that c<0.11(0.13) at 95% (99.7%) confidence limit within a context of a toy model that assumes a perfectly spherical voids with sharp boundaries.Comment: 8 pages, 4 figures; v2 discussion expanded, references fixed, matches version accepted by JCA

Low-noise AlGaAsSb avalanche photodiodes for 1550 nm light detection

Avalanche photodiodes (APD) can improve the signal to noise ratio in applications such as LIDAR, range finding and optical time domain reflectometry. However, APDs operating at eye-safe wavelengths around 1550 nm currently limit the sensitivity because the APDs’ impact ionization coefficients in the avalanche layers are too similar, leading to poor excess noise performance. The material AlGaAsSb has highly dissimilar impact ionization coefficients (with electrons dominating the avalanche gain) so is an excellent avalanche material for 1550 nm wavelength APDs. We previously reported a 1550 nm wavelength AlGaAsSb SAM APD with extremely low excess noise factors, 1.93 at a gain of 10 and 2.94 at a gain of 20. Using a more optimized design, we have now realized an AlGaAsSb SAM APD with a lower dark current (7 nA at a gain of 10 from a 230 μm diameter APD), a higher responsivity (0.97 A/W) and a lower excess noise (1.9 at a gain of 40), compared to our previous SAM APD. Noise-equivalent-power (NEP) measurements of our APD with a simple transimpedance amplifier circuit produced an NEP 12 times lower than a state-of-the-art APD under identical test conditions, confirming the advantage of low-noise AlGaAsSb SAM APDs