Electrostatic interaction between two conducting spheres

In the paper we consider the problem of the electrostatic interaction between two charged conducting spheres with arbitrary electrical charges and radiuses. Using the image charges method we determine exact analytical formulas for the force F and for the potential energy W of the interaction between these two spheres as well as for the potential V of the electromagnetic field in an arbitrary point created by them. Our formulas lead to Coulomb’s law for point charges.We theoretically prove the experimentally shown fact that two spheres with the same type (positive or negative) of charges can also attract each other.     

Influence of Gamma Irradiation on Different Phytochemical Constituents of Dried Rose Hip (Rosa canina L.) Fruits

Gamma irradiation is efficiently applied to many foods, but nevertheless there is a distinct lack of information about the changes of macro- and micronutrients (e.g., carbohydrates, lipids, organic acids, and phenolics) in dried rose hip (RH) fruits. Therefore, in this study, for the first time, the effect of gamma irradiation (10 and 25 kGy) on RH constituents is investigated. Different analytical techniques (GC-FID, HPLC-UV, HPSEC-RID, IR-FT, and SEM) are employed to examine this effect. The irradiation treatment (10 kGy) increased the glucose content by 30% and released cellobiose from RH fruits, thus revealing cellulose destruction. The extractability of total uronic acids increased from 51% (control) to 70.5% (25 kGy-irradiated), resulting in a higher pectin yield (10.8% < 12.8% < 13.4%) and molecular heterogeneity. Moreover, de-esterification was not a major effect of the irradiation-induced degradation of pectin. The sample exposure to the highest dose did not change the content of total carotenoids, β-carotene, and (un)saturated fatty acids, but it affected the tocopherols levels. Gamma rays had a negligible effect on the phenolic constituents and did not affect ORAC and HORAC antioxidant activity. In conclusion, it can be compromised that the exposition of dried RH is safe and can be successfully applied to decontaminate fruits without affecting their nutritional value and biological activity.     

Study on low-cost calibration-free pH sensing with disposable optical sensors

As labor costs become more expensive, less labor-intensive disposable devices have become more ubiquitous. Similarly, the disposable optical pH sensor developed in our lab could provide a convenient yet cost-effective way for pH sensing in processes that require stringent pH control. This optical pH sensor is prepared in uniform individual lots of 100–200 sensors per lot. Calibration is accomplished on a few randomly selected sensors out of each lot. We show that all others in the same lot can then be used directly without requiring individual calibration. In this paper, a calibration model is derived to include all the factors that affect the signal of the disposable sensor. Experimental results show that the derived calibration model fits the experimental data. The readings of 28 randomly selected disposable sensors with 4 sensors from each of the 7 lots show an error less than 0.1 pH units in the useful sensing range of the sensor. The calibration model indicates that if further improvement on precision is desired, more uniform porous material and more advanced coating techniques will be required. When it comes to the effects of the varying coasters, house-made low-cost fluorometers, the variability in the brightness ratio of the blue-to-violet LEDs is the primary reason for the lack of precision. Other factors like LED light intensity distribution, optical properties of the filters and electronics also contribute to the coaster-to-coaster difference, but to a lesser extent. Two different methods for correcting the instrument variations were introduced. After correction, the collective reading errors for all the tested instruments were reduced to less than 0.2 pH units within the sensor's useful sensing range. Based on this result, our lab is currently implementing further improvements in modifying the coasters to equalize the ratios of blue-to-violet LED brightness.     

Synthesis and antibacterial activity of hydroxylated 2-arylbenzothiazole derivatives

Abstract

N-acyliminium reagents formed in situ from benzothiazole and alkyl chloroformates react with hydroxyarenes in a Friedel-Crafts manner, providing access to 2-(hydroxyaryl)-benzothiazolines with antibacterial properties.     

Stability problems of textile wound structures

Mathematical model for calculation of the stress-strain behavior of the wound package is presented. It uses the split of the body of cylindrical layers with finite thickness under assumption for orthotropic, linear elastic behavior of the single layers. The numerical results demonstrate, that in certain cases the windings and layers lose their tension forces, where the winding package loses its stability. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical diffraction by using electrically-controlled spatially patterned nematic pentylcyanobiphenyl films under static electric field

ABSTRACT

Diffractive electro-optics of electrically-induced spatially periodic texture patterns (namely, wide-formed stationary parallel stripes) in planarly-aligned films of the nematic liquid crystal 4-n-pentyl-4′-cyanobiphenyl (5CB) is examined under static electric field in view of its practical application. The longitudinal textural domains electrically-induced with well defined threshold and spatial period have flexo-dielectric nature and differ from the usual flexoelectric stripe distortion, as well as from the electroconvective domains of frequency-dependent morphology. The low-voltage-controlled grating effect through the flexo-dielectric domains can be useful for nematic diffractive optics.     

First Observation of Surface Plasmon-Coupled Emission Due to LED Excitation

Detection limitations for fluorescence methods are normally determined by the phenomenon itself rather than the sensitivity of the instrumentation. These limitations make it necessary to have high sensitivity, high cost equipment causing fluorescence methods to remain lab-oriented. Alleviation of the limitations can be achieved through the phenomenon of surface plasmon-coupled emission (SPCE), which displays enhanced, directional, polarized fluorescence. Here we present the excitation of SPCE from Rhodamine B with a light-emitting diode (LED). Incorporating the gains in sensitivity due to SPCE with LED excitation, it could be possible to design low-cost, high-sensitivity sensors that would allow measurements to be performed in the field.     

Assessment of a Plantibody HB-01 Purification Strategy at Different Scales

Transgenic plant investigations focus on fine-regulation of the recombinant protein expression and purification strategies. In this article, preliminary experiments were done at analytical-scale to decide the best plantibody HB-01 purification strategy. Once it was assumed, the purification efficiency was assessed at different scales (10–600 kg of biomass). The plantibody purity measured by SDS-PAGE and LC-GF was over 90%, yielding 9.9 ± 6.2–18.6 ± 0.9 mg plantibody kg⁻¹ of biomass and 39.9 ± 7.9–48.7 ± 2.1% of recovery. Significant differences were not observed among these parameters at these scales. Plant DNA contents were <3.3 ng mg⁻¹ of plantibody, which is considered very low for the plantibody HB-01 application in the hepatitis B vaccine production.

     

Lensless CCD-based fluorometer using a micromachined optical Söller collimator

In this paper, we describe a simple charge-coupled device (CCD) based lensless fluorometer with sensitivity in the range of current ELISA plate readers. In our lensfree fluorometer, a multi-wavelength LED light source was used for fluorophore excitation. To collimate the light, we developed a simple optical S?ller collimator based on a "stack of pinholes" (a stack of black PMMA with array of pinholes machined with laser) enabling the light to be collimated from the LED through the filters and the assay's microfluidics directly onto the CCD without a lens. The elimination of the lens that is used in almost all other current CCD based detection systems has four major advantages: (1) It simplifies the device design and fabrication while reducing cost. (2) It reduces the distance between the sample and the measuring device (without a lens the distance needed to focus the image on the CCD is reduced and the fluorometer can be more compact). (3) It couples the CCD and the detected surface by using an optical S?ller Collimator which allows the use of filters for fluorescence detection. (4) It also uncouples the CCD and the microfluidics to enable the use of interchangeable fluidics while protecting the delicate CCD. The lensless CCD-based fluorometer is capable of detecting 16 samples simultaneously, and was used for in vitro detection of botulinum neurotoxin serotype A (BoNT-A) activity with a FRET assay that measures cleavage of a fluorophore-tagged peptide substrate specific for BoNT-A (SNAP-25) by the toxin light chain (LcA). The limit of detection (LOD) of our lensless fluorometer is 1.25 nM, which is similar to the LOD of a modern ELISA plate reader. Combined with microfluidics, this simple low cost point-of-care (POC) medical diagnostic system may be useful for the performance of many other complex medical diagnostic assays without a laboratory and thus potentially enhancing the accessibility and the quality of health care delivery in underserved populations.