Performance improvement in Mach–Zehnder interferometer-based refractive index sensor using elliptical photonic nanowires

We propose a modified Mach–Zehnder interferometer design based on elliptical silica photonic nanowires. The use of the interferometer as an evanescent field-based refractive index (RI) sensor was numerically investigated. Single-mode operation, maintaining polarization and very high sensitivity, is achieved at short optical wavelengths by simply using elliptical nanowires. The proposed sensor is capable of determining the RI of benzene solutions with different concentrations in water and detecting a RI variation of the order of 10^?6 RI units in only a 1-mm length sensitive area. Extremely high sensitivity of 4.63?rad/μm is achieved using an 800?nm elliptical silica nanowire diameter. The operating wavelengths (λ = 650?nm and 970?nm) were chosen to avoid high water absorption. The sensor is shown to be an alternative solution to small circular-nanowire-based sensor whose core size needs to be significantly reduced below 400?nm to achieve comparable performance.     

Entropy generation in Poiseuille–Benard channel flow

The issue of entropy generation in Poiseuille–Benard channel flow is analyzed by solving numerically the mass, momentum and energy equations with the use of the classic Boussinesq incompressible approximation. The numerical scheme is based on Control Volume Finite Element Method with the SIMPLER algorithm for pressure–velocity coupling. Results are obtained for Rayleigh numbers Ra and irreversibility φ ranging from 10³ to 5×10⁴ and from 10⁻⁴ to 10 respectively. Variations of entropy generation and the Bejan number as a function of Ra and φ are studied. The limit value φ_l for which entropy generation due to heat transfer is equal to entropy due to fluid friction is evaluated. It has been found that φ_l is a decreasing function of the Rayleigh number Ra. φ_l varies from 0.0015 to 0.096 when Ra decrease from 5×10⁴ to 10³. Stream lines and entropy generation maps are plotted at six times over one period at Ra =10⁴ and φ=10⁻³. It has been found that the maximum entropy generation is localized at areas where heat exchanged between the walls and the flow is maximum. No significant entropy production is seen in the main flow.     

Effect of Plant Originated Coagulants and Chymosin on Ovine Milk Coagulation

The coagulation of ewe's milk was studied by using plant source coagulants namely the artichoke, Cynara scolymus L. cv. Blanca, and latex from the fig tree (Ficus carica L.). A turbidimetric method was used to evaluate and compare the coagulation properties of the novel coagulants with chymosin treated samples. Syneresis capacity and sensory evaluation of resultant cheese samples were studied and it was found that both cynara and chymosin produced sigmoidal increase in turbidity to the milk with three distinct phases. The coagulation kinetics was affected substantially by both coagulants. Plant coagulant induced shorter gelation time compared to chymosin however required longer time for restructuration (end of coagulation). The coagulum obtained with the latex of Ficus carica had a higher yield, owing to its high water retention capacity. With the exception of color, the overall sensory attributes did not show significant differences among coagulants.     

Variations of DOM quality in inflows of a drinking water reservoir: linking of van Krevelen diagrams with EEMF spectra by rank correlation

Elevated concentrations of dissolved organic matter (DOM) such as humic substances in raw water pose significant challenges during the processing of the commercial drinking water supplies. This is a relevant issue in Saxony, Central East Germany, and many other regions worldwide, where drinking water is produced from raw waters with noticeable presence of chromophoric DOM (CDOM), which is assumed to originate from forested watersheds in spring regions of the catchment area. For improved comprehension of DOM molecular composition, the seasonal and spatial variations of humic-like fluorescence and elemental formulas in the catchment area of the Muldenberg reservoir were recorded by excitation emission matrix fluorescence (EEMF) and ultrahigh-resolution mass spectrometry (FT-ICR-MS). The Spearman rank correlation was applied to link the EEMF intensities with exact molecular formulas and their corresponding relative mass peak abundances. Thereby, humic-like fluorescence could be allocated to the pool of oxygen-rich and relatively unsaturated components with stoichiometries similar to those of tannic acids, which are suspected to have a comparatively high disinfection byproduct formation potential associated with the chlorination of raw water. Analogous relationships were established for UV absorption at 254 nm (UV(254)) and dissolved organic carbon (DOC) and compared to the EEMF correlation.     

Dispersion and behavior of hydrogen during a leak in a prismatic cavity

Security is recognized as one of the most important problems facing the wider use of hydrogen and the increased risk of accidental release into the infrastructure. Prismatic cavity design can be represented one of the best solutions for this problem. For this reason, dispersion and accumulation of hydrogen in a prismatic cavity with natural ventilation are computationally investigated by the commercial software FLUENT.     

Numerical investigation of the hydrodynamics of split‐and‐recombination and multilamination microreactors

The hydrodynamics and residence time distribution (RTD) of two microreactors based on the split‐and‐recombination (SAR), and multilamination mixing mechanisms, respectively were investigated. It was found that the design of the distribution manifolds of the SAR mechanism produces an unbalanced flow distribution. For feeding ratios different than one, bypassing and recirculation occur within the SAR manifolds. For equal flow rates the SAR flow behavior can be accurately described by the pure convection model. The manifold used in the multilamination microreactor achieves a homogeneous distribution of flow and its interdigital mixing structure generates an alternated pattern of fluid layers which is maintained for Re < 140. After this point the ordered arrangement is broken and two large segregated zones are formed. In the absence of molecular diffusion both microreactors reach limiting values of scale and intensity of segregation that were found to be independent of the energy applied to the system. © 2012 American Institute of Chemical Engineers AIChE J, 59: 988–1001, 2013     

A 3.1–4.8-GHz direct-conversion mixer in 0.35-μm CMOS for mode-1 MB-OFDM UWB systems

This paper presents a CMOS direct-conversion mixer for TFI-OFDM receiver of UWB group #1 bands, providing a 110 Mbits/s rate and optimized for 0.35-μm technology. The proposed mixer uses the current-bleeding technique in both the driver and switching stages with wideband impedance matching, consisting of a bandpass filter embedding the RF stage. The 1/f noise of the switching pairs dominates the noise performance for down-converted frequencies below 1 MHz. Above 1 MHz, the insertion of an inductor at the tail of switching pairs reduces uniformly the noise figure by 2.2 dB. Over 3.1–4.8 GHz, the circuit drawing 6 mA from 3-V supply, shows a conversion gain of 14.0 ± 1.0 dB, IIP3 of 0 ± 2 dBm, double-sideband noise figure of 4.5–4.8 dB, and port-to-port isolation above 61.0 dB. The mixer output bandwidth is 460 MHz. The RF power and LO amplitude marginally affect these performances within, respectively, the FCC-power limits and 2.5–3.4 V range.     

A High-Performance Doubly-Balanced Mixer in 0.35-μm CMOS for Mode-1 MB-OFDM UWB Receivers

A new design of CMOS doubly-balanced down-conversion mixer intended for Multiband Orthogonal Frequency Division Multiplexing (MB-OFDM) receiver of UWB group#1 bands and optimized for 0.35-μm technology is presented. The proposed mixer uses the current-bleeding technique in both the driver and switching stages with wideband impedance matching, consisting of a bandpass filter embedding the RF stage. The mixer performances are optimized for the AMS 0.35 μm CMOS process parameters. Over 3.1–4.8 GHz, the circuit drawing 6 mA from 3-V supply, shows a conversion gain of 14.0±1.0 dB, IIP3 of 0±2 dBm, doubly-sideband noise figure of 4.5–4.8 dB, and port-to-port isolation above 61.0 dB.

Effect of green and black teas (Camellia sinensis L.) on the characteristic microflora of yogurt during fermentation and refrigerated storage

The effect of tea on the fermentation and survival of yogurt microorganisms was studied. Green and black teas were added to milk at the beginning of fermentation. Acidity of yogurt products and survival of their microflora were studied during 42 days at 4 °C. Results showed that the presence of tea did not significantly (P < 0.05) influence the yogurt characteristic microorganisms. HPLC studies demonstrated that yogurt bacteria did not affect tea catechins when they were incubated together for 48 h. Indeed, all five products reached about 10⁹ CFU/ml after 6 h of fermentation. Viability during 6 weeks storage at 4 °C varied very little (8.35 < log CFU/ml < 8.65). Similarly, green and black teas had no effect on lactic acid levels of the final products (after 6 weeks of storage, acidity remained above 80 °D). According to these findings, addition of teas or tea catechins to yogurt can be recommended to take advantage of their beneficial properties on human health attributed to their antioxidant and antimicrobial activities.