A Streamlined Molecular Biology Module for Undergraduate Biochemistry Labs

Site-directed mutagenesis and other molecular biology techniques, including plasmid manipulation and restriction analysis, are commonly used tools in the biochemistry research laboratory. In redesigning our biochemistry lab curricula, we sought to integrate these techniques into a term-long, project-based course. In the module presented here, students use structural data to design a site-directed mutant and make the mutation using the Ku¨ nkel method. A second, silent mutant, that creates or removes a restriction site, is simultaneously introduced. Restriction digestion and agarose gel electrophoresis are used to assess the success of mutagenesis. Placing these procedures in the context of continuous, studentdriven project serves to create a ‘‘research style’’ laboratory environment

EXIT OF MEAT SLAUGHTER PLANTS DURING IMPLEMENTATION OF THE PR/HACCP REGULATIONS

Implementation of the Pathogen Reduction and Hazard Analysis and Critical Control Points (PR/HACCP) regulations has occurred across all U.S. meat and poultry plants. A probit model is estimated to determine which factors have affected the probability of red meat slaughter plant exit during implementation of the regulations. While controlling for plant-level, company-level, regional-level, and supply conditions that may affect the probability of plant exit, smaller plants are found to exhibit a much greater probability of exit than larger plants. Other factors affecting plant exit include plant age, market share relative to the degree of market concentration, regional entry rates, and state-level wage rates.Agribusiness,

PLANT ENTRY AND EXIT FROM THE MEATPACKING INDUSTRY DURING PATHOGEN REDUCTION AND HACCP IMPLEMENTATION

Implementation of the Pathogen Reduction and Hazard Analysis and Critical Control Points (PR/HACCP) regulations has now occurred across all U.S. meat and poultry plants. Using databases of plants under federal inspection, we estimate a probit model to determine which factors have affected the probability of exit of meat slaughtering plants during implementation of the regulations.Industrial Organization, Livestock Production/Industries,

Dynamics and evaporation of defects in Mott-insulating clusters of boson pairs

Repulsively bound pairs of particles in a lattice governed by the Bose-Hubbard model can form stable incompressible clusters of dimers corresponding to finite-size n=2 Mott insulators. Here we study the dynamics of hole defects in such clusters corresponding to unpaired particles which can resonantly tunnel out of the cluster into the lattice vacuum. Due to bosonic statistics, the unpaired particles have different effective mass inside and outside the cluster, and "evaporation" of hole defects from the cluster boundaries is possible only when their quasi-momenta are within a certain transmission range. We show that quasi-thermalization of hole defects occurs in the presence of catalyzing particle defects which thereby purify the Mott insulating clusters. We study the dynamics of one-dimensional system using analytical techniques and numerically exact t-DMRG simulations. We derive an effective strong-interaction model that enables simulations of the system dynamics for much longer times. We also discuss a more general case of two bosonic species which reduces to the fermionic Hubbard model in the strong interaction limit.Comment: 12 pages, 10 figures, minor update

Steady-state crystallization of Rydberg excitations in an optically driven lattice gas

We study resonant optical excitations of atoms in a one-dimensional lattice to the Rydberg states interacting via the van der Waals potential which suppresses simultaneous excitation of neighboring atoms. Considering two- and three-level excitation schemes, we analyze the dynamics and stationary state of the continuously-driven, dissipative many-body system employing time-dependent density-matrix renormalization group (t-DMRG) simulations. We show that two-level atoms can exhibit only nearest neighbor correlations, while three-level atoms under dark-state resonant driving can develop finite-range crystalline order of Rydberg excitations. We present an approximate rate equation model whose analytic solution yields qualitative understanding of the numerical results.Comment: 5 pages,3 figure

Limiting Behaviour of the Mean Residual Life

In survival or reliability studies, the mean residual life or life expectancy is an important characteristic of the model. Here, we study the limiting behaviour of the mean residual life, and derive an asymptotic expansion which can be used to obtain a good approximation for large values of the time variable. The asymptotic expansion is valid for a quite general class of failure rate distributions--perhaps the largest class that can be expected given that the terms depend only on the failure rate and its derivatives.Comment: 19 page

The Effect of a Target Bite Count and Plate Size on Food Intake.

The purpose of this study was to determine if an instruction to take fewer bites than typically taken, would reduce intake and overcome the known environmental cue of plate size. In a previous study, fifty-five participants (34F) ate ad libitum macaroni and cheese in groups of four, either from a small plate or a large plate. They ate 111±35g with 12±4 bites from the small plate, and 195±111g with 20± 6 bites from the large plate. The current study employed the same paradigm. Sixty participants (33F) were given bite count feedback and were instructed to take only 12 bites, while eating from either a small plate or a large plate. Participants ate 135±52g with 12±3 bites from the small plate and 177±63g with 12±2 bites from the large plate. Results of a 2x2 ANOVA indicate a main effect of plate size (p\u3c.001) and instruction (p\u3c.001) on bites taken and an interaction (p\u3c.001). Plate size also affected grams consumed (p\u3c.001). Notably, instruction also affected bite size (p\u3c.001). These results suggest that people will reduce the number of bites when instructed to, but will increase their bite size to compensate for the reduced bite allowance

Exopolysaccharides Regulate Calcium Flow in Cariogenic Biofilms

Caries-associated biofilms induce loss of calcium from tooth surfaces in the presence of dietary carbohydrates. Exopolysaccharides (EPS) provide a matrix scaffold and an abundance of primary binding sites within biofilms. The role of EPS in binding calcium in cariogenic biofilms is only partially understood. Thus, the aim of the present study is to investigate the relationship between the calcium dissolution rates and calcium tolerance of caries-associated bacteria and yeast as well as to examine the properties of EPS to quantify its binding affinity for dissolved calcium. Calcium dissolution was measured by dissolution zones on Pikovskaya’s agar. Calcium tolerance was assessed by isothermal microcalorimetry (IMC) by adding CaCl2 to the bacterial cultures. Acid-base titration and Fourier transform infrared (FTIR) spectroscopy were used to identify possible functional groups responsible for calcium binding, which was assessed by isothermal titration calorimetry (ITC). Lactobacillus spp. and mutans streptococci demonstrated calcium dissolution in the presence of different carbohydrates. All strains that demonstrated high dissolution rates also revealed higher rates of calcium tolerance by IMC. In addition, acidic functional groups were predominantly identified as possible binding sites for calcium ions by acid-base titration and FTIR. Finally, ITC revealed EPS to have a higher binding affinity for calcium compared, for example, to lactic acid. In conclusion, this study illustrates the role of EPS in terms of the calcium tolerance of cariogenic microbiota by determining the ability of EPS to control free calcium concentrations within the biofilms as a self-regulating mode of action in the pathogenesis of dental caries