Comparison of swab transport media for recovery of Listeria monocytogenes from environmental samples

Environmental monitoring is recognized as an important strategy for controlling Listeria monocytogenes in food processing facilities. Samples are taken by swabbing environmental surfaces, and the swabs are immersed in a medium for transport to the laboratory. In this study, buffered peptone water (BPW), Dey-Engley neutralizing broth (DE), neutralizing buffer (NB), Letheen broth (LE), and newly described MCC buffer (MCC) were evaluated as transport media for recovery of sanitizer-stressed L. monocytogenes from inoculated swabs. After storage at 4°C, the media performed similarly, but at 25°C relative recovery efficiency from the inoculated sponges was DE > LE > BPW > MCC > NB. Recoveries from stainless steel surfaces followed similar trends. MCC, DE, and NB were compared for L. monocytogenes recovery in the presence of Escherichia coli, Enterococcus faecalis, Lactobacillus plantarum, Pseudomonas fluorescens, and Listeria innocua. After 4°C storage, all population levels changed little; after 25°C storage, DE allowed the best growth of L. monocytogenes regardless of other species present. MCC, DE, and NB performed similarly for recovery of L. monocytogenes from an artificial milk biofilm and for recovery of Listeria spp. from swabs obtained from a meat processing facility. Transport medium formulation, time and temperature of swab storage, and coexistence of other species affect recovery of sanitizer-stressed L. monocytogenes from environmental swabs. The study confirms the need to maintain 4°C storage conditions during swab transport.     

DESIGN ASPECTS OF SOLAR THERMOCHEMICAL ENGINEERING—A CASE STUDY: TWO-STEP WATER-SPLITTING CYCLE USING THE Fe3O4/FeO REDOX SYSTEM

We describe a methodology for the initial development of solar thermochemical reactors for converting concentrated solar energy into chemical fuels. It consists of determining the implications that the thermodynamics and kinetics of the chemical transformation have on the initial reactor design. The method is applied for a specific case study: the decomposition of iron oxide above 1875 K, as part of a two-step thermochemical cycle for producing hydrogen from water. We demonstrate that the chemistry of the reaction places important constraints on various engineering design aspects, and we present two reactor concepts that satisfy these constraints. This study addresses the initial steps necessary for the design and development of solar chemical reactors.     

Analysis and Modeling of Energy Consumption in RLC Tree Circuits

In this paper, the energy consumption of resistance-inductance-capacitance (RLC) trees is analytically modeled. In particular, the results obtained by the same authors for RC tree circuits are generalized, allowing for a deep understanding of the impact of the inductance. The modeling approach proposed relies on the adoption of an equivalent second-order RLC circuit, whose energy consumption is evaluated in a closed form. These results are then extended to RLC circuits with arbitrary order, deriving a simple and accurate model. The energy dependence on the input rise time is also analyzed in detail, identifying the ranges for which the RLC circuit can be approximated to a simple capacitance or an RC circuit. The model equations provide an insight into the dependence of the energy consumption on the circuit parameters. Indeed, the energy is explicitly expressed as a function of the resistances, capacitances and inductances of the original network. The energy model proposed is shown to be accurate enough for modeling purposes through comparison with SPICE simulations, as the error is typically in the order of a few percentage points.     

Evidence of the CH···O HydrogenBonding in Imidazolium-Based Ionic Liquids from Far-Infrared Spectroscopy Measurements and DFT Calculations

Knowledge of all the intermolecular forces occurring in ionic liquids (ILs) is essential to master their properties. Aiming at investigating the weaker hydrogen bonding in aprotic liquids, the present work combined computational study and far-infrared spectroscopy on four imidazolium-based ILs with different anions. The DFT calculations of the ionic couples, using the ωB97X-D functional and considering both the empirical dispersion corrections and the presence of a polar solvent, show that, for all samples, the lowest energy configurations of the ion pair present H atoms, directly bound to C atoms of the cation and close to O atoms of the anion, capable of creating moderate to weak hydrogen bonding with anions. For the liquids containing anions of higher bonding ability, the absorption curves generated from the calculated vibrational frequencies and intensities show absorption bands between 100 and 125 cm⁻¹ corresponding to the stretching of the hydrogen bond. These indications are in complete agreement with the presently reported temperature dependence of the far-infrared spectrum, where the stretching modes of the hydrogen bonding are detected only for samples presenting a moderate interaction and become particularly prominent at low temperatures. Moreover, from the analysis of the infrared spectra, the occurrence of various phase transitions as a function of temperature was detected, and the difference in the average energy between the H-bonded and the dispersion-governed molecular configurations was evaluated.     

New CMOS current mirrors with improved high-frequency response

A new CMOS current mirror is presented which has the static characteristic of the cascode current mirror and a high-frequency performance equivalent to or better than that of the simple current mirror. Moreover, the circuit proposed does not present the instability problem of the improved cascode utilized to increase the high-frequency response. The circuit is designed using CMOS 2 μm technology with various aspect ratios and simulated with the SPICE programme.     

Simple and accurate modeling of the output transition time in nanometer CMOS gates

In this paper, a model of the output transition time on nanometer CMOS gates is proposed. The development of this model follows the general approach used by Auvergne in (IEE Electron. Lett. 2002; 38 (4):175–177, IEEE Trans. Circuits Systems—part I 2000; 47 (9):1362–1369, IEEE Proc. ISCAS 2001; 5 :363–366, IEEE Trans. Computer‐Aided Design Integr. Circuits Systems 2002; 21 (11):1352–1363), which separately models the output transition time under fast and slow inputs. The proposed model is based on a combined transient and DC circuit analysis, and requires a few simulations. This approach allows for strongly reducing the number of required parameters and simulations compared with other models proposed in the literature. The analytical model proposed is very simple and has a clear physical meaning, thereby allowing an efficient implementation in CAD tools performing timing analysis, as well as an easy scalability through different processes and technology generations. Spectre simulations on a 65 nm CMOS technology and the 45, 32, 22 nm Berkeley Predictive Technology Models (BPTM) [Berkeley Predictive Technology Model (BPTM). ONLINE@11/25/2008: http://www.eas.asu.edu/～ptm/ ] show that the model accuracy is the same as the state‐of‐the‐art models, with an average error of only 4%. Comparison with currently used table‐based models showed also a significant reduction in the CPU time needed to simulate and characterize CMOS logic gates. Copyright © 2009 John Wiley & Sons, Ltd.     

Biocompatible α-aminoacids based aliphatic polyamides

Summary. Biodegradable aliphatic polyamides have been prepared from C10 and C14 dicarboxylic acids and amide-diamines containing one or two preformed amide linkages susceptible to enzymatic cleavage in their molecules. L-phenylalanine, either by itself or together with L-valine, was used to generated amide bonds which are cleavable by chimotrypsine. Improved chain flexibility and hydrophilicity of the polyamides was obtained using a triethyleneoxy based amide-diamine. Characterization of the novel monomers and polymers by FTIR and ¹H-NMR spectroscopy confirms the expected structures. Thermal data and solubility tests indicate that both T _m and solubility depend on the length and nature of the aliphatic segment present in the amide-diamine as well as on the "density" of interchain hydrogen bonds. Finally the polymers tested are capable of supporting fibroblast adherence and proliferation, and proved to be non cytotoxic. Received: 28 May 1997/Revised: 16 July 1997/Accepted: 16 July 1997     

The torcular Herophili: the diagnostic pitfalls in TOF 3D magnetic resonance angiography

The authors report on a diagnostic pitfall which is often observed in magnetic resonance angiography (MRA) of intracranial vessels (time-of-flight 3D)--i.e., the absence of one of the two transverse sinuses. Fifty patients underwent MRA of the intracranial vessels with the TOF 3D (FISP) and the TOF 2D (FISP) techniques. Five patients were affected with sinus stenosis. MRA was performed with a 1.5-T superconductive magnet and a circular head coil. All patients underwent Magnetic Resonance Angiography with FISP 2D sequences (FA 40 degrees, TR 40 ms, TE 12 ms) acquired on coronal plane as well as FISP 3D (FA 15 degrees, TR 30 ms, TE 7 ms) acquired on axial plane. In the patients in whom FISP 2D sequences correctly demonstrated the whole confluence of sinuses, FISP 3D sequences always depicted the upper sagittal sinus, while the right transverse sinus was seen in 84.4% (38/45) of cases and the left transverse sinus in 24.2% (11/45) of cases. In the patients with a stenosis in the confluence of sinuses, FISP 3D sequences demonstrated two false-positive cases with respect to FISP 2D. The statistical analysis (McNemar test) of the results demonstrated the difference between 2D and 3D sequences in the detection of the two transverse sinuses to be statistically significant: p < 0.01 for the right transverse sinus and p < 0.001 for the left transverse sinus. In the study of the intracranial vessels (TOF 3D technique) the absence of one of the two transverse sinuses is suggestive of a diagnostic pitfall; the combination of 3D and 2D sequences answers this diagnostic question.     

Low-voltage high-drive CMOS current feedback op-amp

A novel CMOS current feedback op-amp is presented. The solution works using a low supply voltage and provides a wide input/output swing as well as a high current driving capability. Experimental results from a prototype implemented in a 0.35-/spl mu/m technology and powered with 1.5 V are also given. The circuit exhibits a better than 500 kHz closed-loop bandwidth and a /spl plusmn/1 mA current drive capability.