Modeling Firm and Market Dynamics: A Flexible Model Reproducing Existing Stylized Facts on Firm Growth

This paper presents a model of firm and market dynamics that is able to reproduce the empirically observed patterns on firm growth and its statistical characteristics. It goes beyond the existing firm models by reproducing all stylized facts established in the literature. Furthermore, the model is flexible in the sense that various parameter settings are identified that reproduce the stylized facts. We identify and discuss different ranges of the model’s parameters that allow for adapting the model to certain industries and life-cycle stages.     

Nonproteolytic Clostridium botulinum toxigenesis in cooked turkey stored under modified atmospheres

The ability of nonproteolytic Clostridium botulinum type B spores to grow and produce toxin in cooked, uncured turkey packaged under modified atmospheres was investigated at refrigeration and mild to moderate abuse temperatures. Cook-in-bag turkey breast was carved into small chunks, surface-inoculated with a mixture of nonproteolytic C. botulinum type B spores, packaged in O2-impermeable bags under two modified atmospheres (100% N2 and 30% CO2:70% N2), and stored at 4, 10, and 15 degrees C. Samples were analyzed for botulinal toxin and indigenous microorganisms, as well as subjected to sensory evaluation, on days 0, 7, 14, 28, 42, and 60. Given sufficient incubation time, nonproteolytic C. botulinum type B grew and produced toxin in all temperature and modified atmosphere treatment combinations. At moderate temperature abuse (15 degrees C), toxin was detected by day 7, independent of packaging atmosphere. At mild temperature abuse (10 degrees C), toxin was detected by day 14, also independent of packaging atmosphere. At refrigeration temperature (4 degrees C), toxin was detected by day 14 in product packaged under 100% N2 and by day 28 in product packaged under 30% CO2:70% N2. Reduced storage temperature significantly delayed toxin production and extended the period of sensory acceptability of cooked turkey, but even strict refrigeration did not prevent growth and toxigenesis by nonproteolytic C. botulinum. At all three storage temperatures, toxin detection preceded or coincided with development of sensory characteristics of spoilage, demonstrating the potential for consumption of toxic product when spoilage-signaling sensory cues are absent.     

Prevalence and determinants of Helicobacter pylori infection in preschool children: a population-based study from Germany

Branching enzyme (BE) belongs to the amylolytic family which contains four highly conserved regions. These regions are proposed to play an important role in catalysis as they are thought to be necessary for catalysis and/or binding the substrate. Only one arginine residue was found to be conserved in a catalytic center at the same position in all known sequences of BEs from various species as well as in the alpha-amylase enzyme family. In mBEII, a conserved Arg residue 384 is in catalytic region 2. We have used site-directed mutagenesis of the Arg-384 residue in order to study its possible role in BE. Previous chemical modification studies (H. Cao and J. Preiss, 1996, J. Prot. Chem. 15, 291-304) suggest that it may play a role in substrate binding. Replacement of Arg-384 by Ala, Ser, Gln, and Glu in the active site caused almost total inactivation. However, a conservative mutation of the conserved Arg-384 by Lys resulted in some residual activity, approximately 5% of the wild-type enzyme. The kinetics of the purified mutant R384K enzyme were investigated and no large effect on the Km of the substrate amylose for BE was observed. Thus, these results suggest that conserved Arg residue 384 in mBEII plays an important role in the catalytic function of BEs but may not be directly involved in substrate binding.     

必需脂肪酸在美容化妆品中的应用

必需脂肪酸（EFAs）可以使皮肤增益，加强细胞膜结构与功能，维持并恢复皮肤天然屏障，预防皮肤刺激和炎症，以及增强细胞膜的通透性。详述了必需脂肪酸的新陈代谢过程和其在美容化妆品中的应用。     

Synthesis and antiapoptotic activity of a novel analogue of the neutral sphingomyelinase inhibitor scyphostatin

The enantioselective synthesis of an analogue of scyphostatin, a potent inhibitor of the neutral sphingomyelinase, is described. The synthesis starts with cyclohexanone and a protected D-serine derivative. The key step is an asymmetric hydroxylation to access a hydroxycyclohexanone, which is transformed into a substituted hydroxycyclohexenone. This is converted into the scyphostatin analogue 14, a chemically and metabolically stabilised compound lacking the epoxy function of the natural congener and carrying a palmitic acid group instead of the native trienoyl residue. An evaluation of the biological activity of 14 revealed neutral sphingomyelinase inhibition in several in vivo test systems (monocytes, macrophages, hepatocytes) monitoring antiapoptotic effects and the inversion of phorbolester-induced translocation of green fluorescent protein labelled kinase (protein kinase C-alpha).     

Integration Concepts for the Fabrication of LTCC Structures

At the Keck Smart Materials Integration Laboratory at Penn State University, low-temperature co-fired ceramic (LTCC) material systems have been used to fabricate a number of devices for a variety of applications. This article presents an overview of the integration of the concepts and materials that we have used to achieve miniaturization and unique device function. Examples of microwave filters, metamaterial antennas, and a dielectrophoretic cell sorter will be presented, with emphasis on device modeling and design, prototype construction methods, and test results.