Static Characterization of InAs/AlGaAs Broadband Self-Assembled Quantum Dot Lasers

The static-characteristics of InAs/AlGaAs broadband self-assembled quantum-dot laser diodes (SAQD-LDs) have been studied to solve the rate equations numerically using fourth-order Runge-Kutta method. Energy level, size, and composition distributions of the InAs/AlGaAs broadband quantum-dots (QDs) are considered and their effects on Static-characteristics are investigated. Simulated results of static-characteristics show that nonlinearity appears in light-current characteristics whereas homogeneous broadening (HB) becomes equal to inhomogeneous broadening (IHB). Slope-efficiency increases as the HB heightens up to the IHB. Exceeding the HB from IHB results in degradation of light-current characteristics. In fact, InAs/AlGaAs broadband SAQD-LD has the best performance when HB is equal to IHB. Light-current characteristics degrade and threshold current increases as the IHB enhances. We also investigate the effects of QD coverage on the laser performance and show that there is an optimum QD coverage in which the SAQD-LD operates with lowest possible threshold current and maximum output power as whatever the QD coverage enhances from that optimum amount, the threshold current increases and slope efficiency decreases. 

Possibility of primordial black holes as the source of gravitational wave events in the advanced LIGO detector

The analysis of gravitational Wave (GW) data from advanced LIGO provides the mass of each companion of binary black holes as the source of GWs. The mass of events corresponding to the binary black holes from GW is above $20$ M$_\odot$ which is much larger than the mass of astrophysical black holes detected by x-ray observations. In this work, we examine primordial black holes (PBHs) as the source of LIGO events. Assuming that $100\%$ of the dark matter is made of PBHs, we estimate the rate at which these objects make binaries, merge, and produce GWs as a function of redshift. The gravitational lensing of GWs by PBHs can also enhance the amplitude of the strain. We simulate GWs sourced by binary PBHs, with the detection threshold of $S/N>10$ for both Livingston and Hanford detectors. For the log-normal mass function of PBHs, we generate the expected distribution of events, compare our results with the observed events, and find the best value of the mass function parameters (i.e., $M_c =25 M_\odot$ and $\sigma=0.6$) in the log-normal mass function. Comparing the expected number of events with the number of observed ones rules out the present-Universe binary formation PBH scenario as the candidate for the source of GW events detected by LIGO.Comment: Final published versio

Forecasting with auxiliary information in forecasts using multivariate singular spectrum analysis

The internet gives us free access to a variety of published forecasts. Motivated by this increasing availability of data, we seek to determine whether there is a possibility of exploiting auxiliary information contained within a given forecast to generate a new and more accurate forecast. The proposed theoretical concept requires a multivariate model which can consider data with different series lengths as forecasts are predictions into the future. Following applications which consider published forecasts generated via unknown time series models and forecasts from univariate models, we achieve promising results whereby the proposed multivariate approach succeeds in extracting the auxiliary information in a given forecast for generating a new and more accurate forecast, along with statistically significant accuracy gains in certain cases. In addition, the impact of filtering and the use of Google Trends within the proposed methodology is also considered. Overall, we find conclusive evidence which suggests a sound opportunity to exploit the forecastability of auxiliary information contained within existing forecasts

Gravity on Noncommutative D-Branes

The effective action for the low energy scattering of two gravitons with a D-brane in the presence of a constant antisytmetric $B$ field in bosonic string theory is calculated and the modification to the standard D-brane action to first order in $\alpha'$ is obtained.Comment: 18 pages, Latex file, accepted in Int. J. Mod. Phys.

Stabilization of Sand with Colloidal Nano-Silica Hydrosols

Colloidal nano-silica (NS) hydrosols are electrochemically stabilized, polymerized amorphous silica in low viscosity solutions, and in the form of hydrated gels, silica globules or pellicles. Compared to applications in concrete technology, the use of silica-based binders for groundwork applications has received little attention. Silica-based hydrosols impose no known direct risks to humans and are generally courteous to the soil health and ecosystem service functions. Their localized impact on microorganisms however needs to be further investigated. To this end, NS hydrosols have a scope for use as an alternative low-viscose material in groundworks. The current understanding of interactions between NS hydrosols and soil (sand) is, however, confused by the limited availability of experimental evidence concerning undrained static flow and large strain behavior. The contributions, presented in this paper, advance the knowledge through experimental testing, molecular modelling, and micro-analytical measurements. Four grades of colloidal NS (1–15 wt.%) were synthesized for grouting medium-dense sub-angular fine siliceous sand specimens. Consolidated-undrained triaxial compression testing was performed on the base and treated sand for isotropic consolidation over the effective stress range 100–400 kPa. Overall, silica impregnation produced improvements in yield and residual undrained shear strengths, restricted unwelcomed impacts of excess pore water pressure, and led to the formation of generally more dilative, strain-hardening behavior. Steady states and static flow potential indices are also studied as functions of confinement level and viscosity of the NS grout

New Approaches to Analyze Gasoline Rationing

In this paper, the relation among factors in the road transportation sector from March, 2005 to March, 2011 is analyzed. Most of the previous studies have economical point of view on gasoline consumption. Here, a new approach is proposed in which different data mining techniques are used to extract meaningful relations between the aforementioned factors. The main and dependent factor is gasoline consumption. First, the data gathered from different organizations is analyzed by feature selection algorithm to investigate how many of these independent factors have influential effect on the dependent factor. A few of these factors were determined as unimportant and were deleted from the analysis. Two association rule mining algorithms, Apriori and Carma are used to analyze these data. These data which are continuous cannot be handled by these two algorithms. Therefore, the two-step clustering algorithm is used to discretize the data. Association rule mining analysis shows that fewer vehicles, gasoline rationing, and high taxi trips are the main factors that caused low gasoline consumption. Carma results show that the number of taxi trips increase after gasoline rationing. Results also showed that Carma can reach all rules that are achieved by Apriori algorithm. Finaly it showed that association rule mining algorithm results are more informative than statistical correlation analysis

A quantitative exploration of the statistical and mathematical knowledge of university entrants into a UK Management School

Mathematical and statistical skills are increasingly important for securing fruitful employment in the modern world. Regardless of the increasing demand for such skills by employers, witnessed at present is a drop in the mathematics and statistics knowledge of university entrants. This paper uses a British university as a case study and exploits the induction week to collect primary data on the mathematical and statistical knowledge of entrants into two degree programmes. The data is then analysed using statistical techniques to identify the current patterns relating to the mathematics and statistics knowledge of students with a view to developing appropriate methods for enhancing their mathematical and statistical knowledge. Our findings indicate statistically significant differences in the mathematical and statistical knowledge of students entering this British university based on the chosen degree programme, gender and educational qualifications

The absence of the Kerr black hole in the Ho\v{r}ava-Lifshitz gravity

We show that the Kerr metric does not exist as a fully rotating black hole solution to the modified Ho\v{r}ava-Lifshitz (HL) gravity with $\Lambda_W=0$ and $\lambda=1$ case. We perform it by showing that the Kerr metric does not satisfy full equations derived from the modified HL gravity.Comment: 35 pages, no figure