Hasil untuk "physics.comp-ph"

Johanna Langner, Anjan Sadhukhan, Jayanta K. Saha et al.

The application of the stabilization method [A.~U.\ Hazi and H.~S.\ Taylor, Phys.~Rev.~A {\bf 1}, 1109 (1970)]) to extract accurate energy and lifetimes of resonance states is challenging: The process requires labor-intensive numerical manipulation of a large number of eigenvalues of a parameter-dependent Hamiltonian matrix, followed by a fitting procedure. In this article, we present \dosmax, an efficient algorithm implemented as an open-access \texttt{Python} code, which offers full automation of the stabilization diagram analysis in a user-friendly environment while maintaining high numerical precision of the computed resonance characteristics. As a test case, we use \dosmax to analyze the natural parity doubly-excited resonance states (${}^{1}\textnormal{S}^{\textnormal{e}}$, ${}^{3}\textnormal{S}^{\textnormal{e}}$, ${}^{1}\textnormal{P}^{\textnormal{o}}$, and ${}^{3}\textnormal{P}^{\textnormal{o}}$) of helium, demonstrating the accuracy and efficiency of the developed methodology. The presented algorithm is applicable to a wide range of resonances in atomic, molecular, and nuclear systems.

Swarnabha Chattaraj, Supratik Guha, Giulia Galli

We present a predictive and general approach to investigate near-field energy transfer processes between localized defects in semiconductors, which couples first principle electronic structure calculations and a nonrelativistic quantum electrodynamics description of photons in the weak-coupling regime. We apply our approach to investigate an exemplar point defect in an oxide, the F center in MgO, and we show that the energy transfer from a magnetic source, e.g., a rare earth impurity, to the vacancy can lead to spin non conserving long-lived excitation that are dominant processes in the near field, at distances relevant to the design of photonic devices and ultra-high dense memories. We also define a descriptor for coherent energy transfer to predict geometrical configurations of emitters to enable long-lived excitations, that are useful to design optical memories in semiconductor and insulators.

M. Kühl, Y. Cohen, T. Dalsgaard et al.

W. Wilfinger, Karol Mackey, P. Chomczyński

The ratio of absorbance at 260 and 280 nm (the A260/280 ratio) is frequently used to assess the purity of RNA and DNA preparations. Data presented in this report demonstrate significant variability in the RNA A260/280 ratio when different sources of water were used to perform the spectrophotometric determinations. Adjusting the pH of water used for spectrophotometric analysis from approximately 5.4 to a slightly alkaline pH of 7.5-8.5 significantly increased RNA A260/280 ratios from approximately 1.5 to 2.0. Our studies revealed that changes in both the pH and ionic strength of the spectrophotometric solution influenced the A260/280 ratios. In addition, the ability to detect protein contamination was significantly improved when RNA was spectrophotometrically analyzed in an alkaline solution. UV spectral scans showed that the 260-nm RNA absorbance maximum observed in water was shifted by 2 nm to a lower wavelength when determinations were carried out in Na2HPO4 buffer at a pH of 8.5. We found RNA A260/280 ratios to be more reliable and reproducible when these spectrophotometric measurements were performed at pH 8.0-8.5 in 1-3 mM Na2HPO4 buffer.

Kangtaek Lee, S. Asher

J. Whalen, Chi Chang, G. Clayton et al.

Mingchun Zhao, M. Liu, G. Song et al.

E. Ajandouz, L. Tchiakpe, F. Oré et al.

G. Rudenko, L. Henry, K. Henderson et al.

M. Qiao, D. L. Fletcher, D. P. Smith et al.

The relationship between broiler breast meat color and pH, moisture content, water-holding capacity (WHC), and emulsification capacity (EC) was investigated. In each of three replicate trials, fillets were collected from three different commercial processing plants according to breast meat lightness (L*) values as follows: lighter than normal (light, L* > 53), normal (48 < L* < 53), and darker than normal (dark, L* < 46). Color values of lightness (L*), redness (a*), and yellowness (b*) were measured at 0 and 24 h after collection. Fillets were then ground and homogenized prior to determining color, pH, moisture, WHC, and EC of the ground meat. There was a significant difference among the three color groups (light, normal, and dark) in L*, a*, pH, WHC, and EC. The L* values of whole raw breast fillets had significant negative correlation coefficients with ground meat EC (-0.9237), pH (-0.9610), and a* (-0.6540). Emulsification capacity had significant positive correlations with pH (0.9572) and water-holding capacity (0.7080). WHC had significant correlations with a* (0.8143), moisture (-0.7647), and pH (0.7963). Lighter-than-normal meat was associated with low pH, high moisture, low EC, and low WHC. These results indicate that wide differences in raw breast meat color exist and that these differences may be used by poultry further processors as an indicator of fillets with altered functional properties.

N. Nelson, R. Mikkelsen, D. Hesterberg

Qing Yang, Shichao Wang, Peiwei Fan et al.

Xiantao Li

We present embedding procedures for the non-Markovian stochastic Schrödinger equations, arising from studies of quantum systems coupled with bath environments. By introducing auxiliary wave functions, it is demonstrated that the non-Markovian dynamics can be embedded in extended, but Markovian, stochastic models. Two embedding procedures are presented. The first method leads to nonlinear stochastic equations, the implementation of which is much more efficient than the non-Markovian stochastic Schrödinger equations. The stochastic Schrödinger equations obtained from the second procedure involve more auxiliary wave functions, but the equations are linear, and we derive the corresponding generalized quantum master equation for the density-matrix. The accuracy of the embedded models is ensured by fitting to the power spectrum. The stochastic force is represented using a linear superposition of Ornstein-Uhlenbeck processes, which are incorporated as multiplicative noise in the auxiliary Schrödinger equations. The asymptotic behavior of the spectral density in the low frequency regime is preserved by using correlated stochastic processes. The approximations are verified by using a spin-boson system as a test example.

Xiao Shi, Yun Shang, Chu Guo

Matrix product state has become the algorithm of choice when studying one-dimensional interacting quantum many-body systems, which demonstrates to be able to explore the most relevant portion of the exponentially large quantum Hilbert space and find accurate solutions. Here we propose a quantum inspired K-means clustering algorithm which first maps the classical data into quantum states represented as matrix product states, and then minimize the loss function using the variational matrix product states method in the enlarged space. We demonstrate the performance of this algorithm by applying it to several commonly used machine learning datasets and show that this algorithm could reach higher prediction accuracies and that it is less likely to be trapped in local minima compared to the classical K-means algorithm.

A. Park, L. Fan

A. Pol, K. Heijmans, H. Harhangi et al.

D. Bhumkar, V. Pokharkar

M. Peñalva, J. Tilburn, E. Bignell et al.

Gavin A. Buxton

A computer simulation is used to predict the effects of membrane morphology on the thermal efficiency of direct contact membrane distillation. The mass transfer through the porous microstructure and the heat conduction through the membrane are both related by the membrane morphology. The interrelated tortuosity of the porous structure and solid phase influences the mass transfer and thermal conductivity, respectively. The effects of varying the morphology are elucidated and introducing a lattice structure, which tailors the morphology, can significantly increase thermal efficiency. A three-layer system is also simulated, where the pore size in the middle layer can be increased without significantly increasing the risk of membrane pore wetting. Three-layer systems that possess a lattice morphology are found to result in thermal efficiencies around 20\% higher than random morphologies.

Jannis Teunissen

Drift-diffusion plasma fluid models are commonly used to simulate electric discharges. Such models can computationally be very efficient if they are combined with explicit time integration. This paper deals with two issues that often arise with such models. First, a high plasma conductivity can severely limit the time step. A fully explicit method to overcome this limitation is presented. This method is compared to the existing semi-implicit method, and it is shown to have several advantages. A second issue is specific to models with the local field approximation. Near strong density and electric field gradients, electrons can diffuse parallel to the field, and unphysically generate ionization. Existing and new approaches to correct this behavior are compared. Details on the implementation of the models and the various approaches are provided.