Dwell time of a Brownian molecule in a microdomain with traps and a small hole on the boundary

We calculate the mean time a Brownian particle spends in a domain with traps and the number of bonds it makes before escaping through a small hole in the boundary. This mean time, called the Dwell time, depends on the backward binding rate (with the trap, e.g., scaffolding molecules), the mean time to reach the trap (forward binding rate), and the size of the hole. We estimate the mean and variance of the number of bonds made prior to exit. In a biochemical context, a quantitative signal occurs when the mean number of bonds exceeds a certain threshold, which may initiate a cascade of chemical reactions that have physiological consequences. We apply the present results to obtain estimates of the mean time a Brownian receptor spends inside a synaptic domain, when it moves freely by lateral diffusion on the membrane of a neuron and interacts at a synapse with scaffolding molecules.     

Synthesis and evaluation of a pseudocyclic tristhiourea-based anion host

A novel methodology for the evaluation of receptor arrangement in structurally flexible anion chemosensors was developed and applied to map the binding site of a new pseudocyclic tristhiourea chemosensor (6). The syntheses of 6 and related macrocyclic chemosensor 10 (a model of the folded monomeric structure of 6) are reported. Both chemosensors were evaluated by titration with a variety of structurally different anions in CH3Cl and DMSO, showing a common preference for F-, CH3CO2-, and H2PO4-. However, within this group of anions, the binding patterns of the chemosensors differed, indicating dissimilarity in the arrangement of the binding sites of 6 and 10.     

Complexity measures of sign matrices

In this paper we consider four previously known parameters of sign matrices from a complexity-theoretic perspective. The main technical contributions are tight (or nearly tight) inequalities that we establish among these parameters. Several new open problems are raised as well. Supported by the ISF. Supported by the ARC.     

Deactivation efficiency of stabilized bactericidal emulsions

Biocide emulsions stabilized with various stabilizing agents were prepared and characterized, and their efficiency in bacteria deactivation was evaluated. A number of stabilizing agents were tested for their stabilizing effect on emulsions of thiocyanomethylthiobenzothiazole (TCMTB) biocide. Two agents, the most successful in stabilizing the biocide, were chosen for further studies: high molecular weight polyethyleneimine (PEI) and an amphiphilic block copolymer of poly(caprolactone)-b-poly(acrylic acid) (PCL(33)-b-PAA(33)). The emulsion droplet sizes varied between 325 and 500 nm. Deactivation of bacteria was studied by exposing E. coli ATCC 11229 bacteria dispersions to emulsions stabilized by positively charged PEI or negatively charged PCL-b-PAA micelles and by measuring their absorbance; E. coli do not grow with time in the presence of biocide emulsions. PEI molecules alone act as biocide and deactivate the bacteria. PCL-b-PAA micelles as stabilizing agent do not affect the growth of the E. coli ; bacteria are deactivated by TCMTB released from the emulsion droplets. The kinetics of emulsion dissolution studies revealed for both stabilizing agents a decrease in droplet size with time while the emulsions were subjected to dialysis. The biocide was released from the emulsions within ～250 min; the droplet shells consist mostly of PEI or PCL-b-PAA insoluble complexes with the biocide, which do not dissolve during dialysis. SEM images confirm the presence of residual crumbled shells with holes after 24 h of dialysis.     

Assessment of Immune Response and Efficacy of Essential Oils Application on Controlling Necrotic Enteritis Induced by Clostridium perfringens in Broiler Chickens

Necrotic enteritis (NE) caused by Clostridium perfringens is one of the most important enteric diseases in poultry. The antibacterial activity of two different essential oil (EO) blends against C. perfringens was investigated both in vitro and in vivo. Additionally, the immunological response to EO treatment was assessed. In the in vitro study, the antibacterial activity of EO formulas and commonly used antibiotics was evaluated against C. perfringens using disk diffusion assay, minimum inhibitory concentration (MIC) assay, and minimum bactericidal concentration (MBC) assay. In the in vivo study, NE experimental infection was performed on 440 Ross broiler chicks at 19 days of age for 4 continuous days. The chicks were treated with either EOs or amoxicillin at 22 days of age for 5 continuous days. One day after the end of treatment, the birds’ performance was evaluated by calculating the feed conversion ratio. Serum samples from 120 birds were collected to measure the levels of IL-1β, IFN-γ, IL-8, IL-10, and IL-17. After that, all birds were slaughtered, and their small intestines were subjected to gross and histopathological evaluation. In addition, bacterial counts in the small intestines were evaluated. In the in vitro study, EOs showed higher antimicrobial activities in comparison with antibiotics against C. perfringens. In the in vivo study, birds treated with EOs showed a significant decrease in bacterial counts, a significant decrease in intestinal lesions, and a significant improvement in performance compared with untreated birds (p < 0.05). Moreover, treating birds with EOs directed the immune system toward an anti-inflammatory pathway. None of the treated birds died due to NE compared with the 10% mortality rate in untreated birds. In conclusion, EOs might be an effective and safe alternative to antibiotics in the treatment of chicken NE.     

Effects of acyl donor type, catalyst type, and reaction conditions on the activity and selectivity of Friedel-Crafts acylation

Acylation of anisole and 3-methylanisole was performed with several acylating reagents (acetylation by AcCl and Ac₂O and bromoacetylation by BrAcCl and (BrAc)₂O) over different solid acid catalysts. The reaction conditions were optimized with respect to the acylation reagent, overall yield, solid acid catalyst, and the products selectivities. While acylation of anisole with acetyl chloride or acetic anhydride resulted in its full conversion to para-substituted acetophenone, the use of bromoacetyl bromide or bromoacetic anhydride yielded also the ortho-substituted product. Acylation of 3-methylanisole also yielded both para- and ortho-substitutions, and the products distribution was affected by the reaction conditions and catalyst type. It was found that while more acidic catalysts (caesium salt of heteropolyacid and zeolites) were the most active towards anisole acylation, the most active catalysts for the acylation of 3-methylanisole were ion-exchange catalysts. Employing HY-740 zeolite resulted in the highest ortho-selectivity in the acylation of anisole with bromoacetyl bromide and bromoacetic anhydride and in the acylation of 3-methylanisole with acetic anhydride.     

Multiple vesicular morphologies from block copolymers in solution

It has been found that asymmetric, amphiphilic diblock copolymers can form a wide range of vesicle architectures in solution. These include small uniform vesicles, large polydisperse vesicles, entrapped vesicles, hollow concentric vesicles, onions, and vesicles with hollow tubes in the walls. The experimental conditions required for preparation and the proposed mechanisms for the formation of each type of structure are discussed.     

Effect of spatial heterogeneity on level of rejuvenation in Ni80P20 metallic glass

Understanding the relation between spatial heterogeneity and structural rejuvenation is one of the hottest topics in the field of metallic glasses (MGs). In this work, molecular dynamics (MD) simulation is implemented to discover the effects of initial spatial heterogeneity on the level of rejuvenation in the Ni$_{80}$P$_{20 }$MGs. For this purpose, the samples are prepared with cooling rates of $10^{10}$ K/s-$10^{12}$ K/s to make glassy alloys with different atomic configurations. Firstly, it is found that the increase in the cooling rate leads the Gaussian-type shear modulus distribution to widen, indicating the aggregations in both elastically soft and hard regions. After the primary evaluations, the elastostatic loading is also used to transform structural rejuvenation into the atomic configurations. The results indicate that the sample with intermediate structural heterogeneity prepared with 10$^{11}$ K/s exhibits the maximum structural rejuvenation which is due to the fact that the atomic configuration in an intermediate structure contains more potential sites for generating the maximum atomic rearrangement and loosely packed regions under an external excitation. The features of atomic rearrangement and structural changes under the rejuvenation process are discussed in detail.     

Miscibility enhancement in polymers via ionic interactions: Dynamic mechanical and NMR studies

The presence of ionic interactions can be used to control the degree of miscibility of otherwise immiscible polymer systems. This control, in turn, allows one to prepare blends with a very wide range of “tailor-made” properties. Several examples are cited. In some of these, the interactions are based on proton transfer from a donor site on one polymer to an aceptor site on another leading to ion-ion interactions. In others, the transfer of a metal cation from an ionomer to a polar polymer, as a result of ion-dipole interactions, is involved. Systems studied to date include, among others, mixtures of polystyrene with poly(ethyl acrylate), polyisoprene, segmented poly urethanes, poly(ethyleneimine), and poly(ethylene oxide). The polyurethane blends with polystyrene are discussed in some detail, focussing especially on the mechanism of miscibility enhancement as determined by NMR. This technique has also been utilised to study the dynamics of the coil overlap process in solution as well as the proximity of the polymer coils to each other. Two particularly noteworthy applications involve mixtures of poly (tetrafluoroethylene) (PTFE) or of phenylated poly(phenylene oxide) with poly (ethyl acrylate), which are also discussed in some detail. Blends of this type may be of special interest in membrane applications.     

A Lyapounov function approach to the theory of stability in a laser using the Scully-Lamb theory

The stability of a quantum model of a c.w. laser is demonstrated using Lyapounov's second method.