Predicting fluid phase equilibrium via histogram reweighting with Gibbs ensemble Monte Carlo simulations

One of the most challenging areas to which molecular simulation has contributed significantly over the last decades is without a doubt the accurate and efficient prediction of fluid phase equilibria. In this work we combine two of the most powerful methods that have greatly enhanced our ability to simulate accurately fluid phase equilibria: (a) the “Gibbs ensemble” method (A.Z. Panagiotopoulos, Molecular Physics 61 (1987) 813-826) and (b) the multiple histogram method (A.M. Ferrenberg, R.H. Swendsen, Physical Review Letters 61 (1988) 2635-2638). The result of such combination is a simple and very accurate method of predicting fluid phase equilibrium close to and away from the critical point.     

The effects of local structural relaxation on aluminum siting within H-ZSM-5

Semiempirical molecular orbital calculations have been performed to study aluminum siting in H-ZSM-5 zeolites. Local structural rearrangements upon substituting aluminum (with a charge compensating proton) for silicon are found to be important. The T12 site is found to be the most preferred site for aluminum substitution. However, the calculated energetics for substitution show that several tetrahedral sites are energetically comparable with regard to aluminum siting. Results pertaining to the electronic properties of the acidic site upon aluminum substitution at each of the twelve distinct tetrahedral sites are presented. The acidic center is found to be a rather soft species, with the HOMO-LUMO energy gap being roughly 8 eV.     

Computation of the stability margin of two-dimensional discretesystems

Two methods of computing the stability margin of two-dimensional discrete systems are presented. The first method uses the Schur-Cohn stability criterion, and the second method is based on results concerning the 1-D Lyapunov equation with complex coefficients. Several examples illustrate the applicability of the two methods     

From dynamic movement primitives to associative skill memories

In recent years, research on movement primitives has gained increasing popularity. The original goals of movement primitives are based on the desire to have a sufficiently rich and abstract representation for movement generation, which allows for efficient teaching, trial-and-error learning, and generalization of motor skills (Schaal 1999). Thus, motor skills in robots should be acquired in a natural dialog with humans, e.g., by imitation learning and shaping, while skill refinement and generalization should be accomplished autonomously by the robot. Such a scenario resembles the way we teach children and connects to the bigger question of how the human brain accomplishes skill learning. In this paper, we review how a particular computational approach to movement primitives, called dynamic movement primitives, can contribute to learning motor skills. We will address imitation learning, generalization, trial-and-error learning by reinforcement learning, movement recognition, and control based on movement primitives. But we also want to go beyond the standard goals of movement primitives. The stereotypical movement generation with movement primitives entails predicting of sensory events in the environment. Indeed, all the sensory events associated with a movement primitive form an associative skill memory that has the potential of forming a most powerful representation of a complete motor skill.     

Evidence of a role for plant proteases in the degradation of herbage proteins in the rumen of grazing cattle

Protein breakdown in the rumen is generally regarded as a two-stage process in which proteases produced by rumen microorganisms cleave plant protein into peptides and amino acids. However, many of the fiber-degrading cellulolytic species in the rumen are not in fact proteolytic, and the proteolytic activity of the entire rumen microbial population is only moderate when compared to the gastric and pancreatic secretions in the abomasum. Moreover, plant cell walls remain largely intact after initial chewing (particularly in cattle), presenting a physical barrier that must be breached prior to their effective colonization. The present study considers the hypothesis that the plant enzymes are at least partly responsible for herbage protein degradation in grazing ruminants. Ryegrass, red clover, white clover, and bird's-foot trefoil were incubated in the presence and absence of rumen microorganisms. The production of volatile fatty acids indicated the level of microbial activity, whereas the relative disappearance of the large subunit of ribulose 1,5 bisphosphate carboxylase/oxygenase (Rubisco LSU) indicated proteolytic activity. In all incubations, the relative abundance of the Rubisco LSU decreased as the incubation progressed. When rumen microorganisms were absent, low molecular weight peptides (below 20 kDa) accumulated as the incubation progressed. This accumulation was not observed in the presence of rumen microorganisms. Therefore we suggest that the intrinsic plant proteases contribute to the initial stages of proteolysis of grazed herbage.     

Radiation dose optimisation and risk estimation to patients and staff during hysterosalpingography

Hysterosalpingography (HSG) is an efficient radiological examination for the evaluation of the female reproductive tract. However, it involves unavoidable irradiation to the ovaries of women in childbearing age. Therefore, radiation dose optimisation is required in order to reduce the probability of the associated risks. This study attempts to: measure patient and staff doses, estimate the effective dose and radiation risk for HSG using digital fluoroscopic images. Thirty-seven patients with infertility were examined using two digital X-ray machines. Thermoluminescence dosimeters (TLD) were used to measure entrance surface dose (ESD) for patients and staff during the procedure. The mean ESD and thyroid surface dose of the patient were 3.60 and 0.17 mGy, respectively, while the mean ESD for the staff was 0.18 mGy per procedure. The patient overall risk for cancer and hereditary effects is 24 x 10(-6), while the risk for the staff is negligible. HSG with fluoroscopic technique demonstrate improved dose characteristics, compared to the conventional radiographic-based technique, reducing the surface dose by a factor of 3, without compromising the diagnostic findings.     

An Arduino based automatic pressure evaluation system to quantify growth of non-model anaerobes in culture

Measuring the growth rate of non-model anaerobic microbes typically requires the use of time-consuming and often destructive manual measurements. Here, an Arduino based automatic pressure evaluation system (A-APES) was developed to automatically measure the rate of fermentation gas production as a proxy for microbial growth in anaerobic systems. The A-APES system measures accumulated gas pressure in sealed cultures accurately at high-resolution, while venting the system at programmed intervals to prevent over pressurization. The utility of A-APES is demonstrated in this study by quantifying the growth rate and phases of a biomass-degrading anaerobic gut fungus, which cannot be otherwise measured via conventional techniques due to its association with particulate substrates. Given the utility of the A-APES approach, we provide a complete construction guide to fabricate the device, which is three times less expensive compared to existing commercial alternatives.     

Stochastic spatio-temporal optimization for control and co-design of systems in robotics and applied physics

Autonomous Robots - Correlated with the trend of increasing degrees of freedom in robotic systems is a similar trend of rising interest in spatio-temporal systems described by partial differential...     

Short communication: Oxidative status and incidence of mastitis relative to blood α-tocopherol concentrations in the postpartum period in dairy cows

Vitamin E supplementation, when combined with high blood α-tocopherol (>6.25 μg/mL) at dry off, has been reported to unexpectedly increased the risk for clinical mastitis in dairy cows. Furthermore, higher levels of oxidative stress in the postpartum period were related to higher risk of mastitis. The objective of the present study was to determine the relationship between various serum biomarkers of oxidative status, incidence of mastitis, and blood α-tocopherol concentrations at dry off and at calving. A total of 146 dairy cows from a commercial farm were used in an observational field study. All cows were supplemented with 3,000 and 50 IU/cow per day of all-rac-α-tocopherol during the dry period and lactation, respectively. Blood samples were collected at dry off and at calving. Serum was analyzed for α-tocopherol, levels of reactive oxygen metabolites (ROM), thiol groups (SH), and ferric-reducing ability. Three α-tocopherol groups at calving were created: high (>3 μg/mL), medium (2–3 μg/mL), and low (<2 μg/mL). Three α-tocopherol groups at dry off were created: high (>6.25 μg/mL), medium (4.25–6.25 μg/mL), and low (<4.25 μg/mL). All cases of clinical mastitis that occurred during the dry period and the entire subsequent lactation were verified by a veterinarian. No differences were observed in the incidence of mastitis between the 3 α-tocopherol groups based on the serum levels at dry off. Incidence of mastitis was 4 times lower in the high and medium groups when compared with the corresponding value for the low-α-tocopherol group based on the serum levels at calving. Lower levels of ROM and SH at dry off and at calving were found in the group of cows with the highest α-tocopherol values at dry off when compared with the corresponding values in the low-α-tocopherol group. The ROM values at dry off but not at calving were lower in the group of cows with the highest α-tocopherol values at calving when compared with the corresponding values in the low-α-tocopherol group. No differences were observed in ferric-reducing ability values between the 3 α-tocopherol groups at dry off or calving. No differences were observed in all biomarkers of oxidative status between healthy cows and those with mastitis. Thus, blood α-tocopherol is inversely related to certain biomarkers of oxidative stress in the postpartum period and incidence of mastitis. However, reduction in the incidence of mastitis is not mediated through a reduction in the levels of various biomarkers of oxidative stress.