Differential reflectance modulation sensing with diffractive microstructures

We present a method for differential ratiometric measurement of reflectance change due to molecular adsorption using a diffractive microstructure fabricated on a reflectance contrast enhancing substrate for bulk refractometry and surface molecular binding detection applications. The differential method suppresses signal fluctuations due to thermal or concentration gradients in the sample flow cell by more than 40x and enables the real-time measurement of molecular interactions on the surface with a noise floor of about 70 pm. (V)C 2012 American Institute of Physics. http://dx.doi.org/10.1063/1.4766190]

Generalizing the Amplify-and-Forward Relay Gain Model: An Optimal SEP Perspective

Two models for AF relaying, namely, fixed gain and fixed power relaying, have been extensively studied in the literature given their ability to harness spatial diversity. In fixed gain relaying, the relay gain is fixed but its transmit power varies as a function of the source-relay channel gain. In fixed power relaying, the relay transmit power is fixed, but its gain varies. We revisit and generalize the fundamental two-hop AF relaying model. We present an optimal scheme in which an average power constrained AF relay adapts its gain and transmit power to minimize the symbol error probability (SEP) at the destination. Also derived are insightful and practically amenable closed-form bounds for the optimal relay gain. We then analyze the SEP of MPSK, derive tight bounds for it, and characterize the diversity order for Rayleigh fading. Also derived is an SEP approximation that is accurate to within 0.1 dB. Extensive results show that the scheme yields significant energy savings of 2.0-7.7 dB at the source and relay. Optimal relay placement for the proposed scheme is also characterized, and is different from fixed gain or power relaying. Generalizations to MQAM and other fading distributions are also discussed.

Space-vector-based hybrid pulse width modulation technique to reduce line current distortion in induction motor drives

Pulse width modulation (PWM) techniques involving different switching sequences are used in space vector-based PWM generation for reducing line current ripple in induction motor drives. This study proposes a hybrid PWM technique employing five switching sequences. The proposed technique is a combination of continuous PWM, discontinuous PWM (DPWM) and advanced bus clamping PWM methods. Performance of the proposed PWM technique is evaluated and compared with those of the existing techniques on a constant volts per hertz induction motor drive. In terms of total harmonic distortion in the line current, the proposed method is shown to be superior to both conventional space vector PWM (CSVPWM) and DPWM over a fundamental frequency range of 32-50 Hz at a given average switching frequency. The reduction in harmonic distortion is about 42% over CSVPWM at the rated speed of the drive.

NMR Analysis of Cross Strand Aromatic Interactions in an 8 Residue Hairpin and a 14 Residue Three Stranded beta-Sheet Peptide

Cross strand aromatic interactions between a facing pair of phenylalanine residues in antiparallel beta-sheet structures have been probed using two structurally defined model peptides. The octapeptide Boc-(LFVPPLFV)-P-D-P-L-OMe (peptide 1) favors the beta-hairpin conformation nucleated by the type II' beta-turn formed by the (D)Pro-(L)Pro segment, placing Phe2 and Phe7 side chains in proximity. Two centrally positioned (D)Pro-(L)Pro segments facilitate the three stranded beta-sheet formation in the 14 residue peptide Boc-LFV(D)P(L)PLFVA(D)P(L)PLFV-OMe (peptide 2) in which the Phe2/Phe7 orientations are similar to that in the octapeptide. The anticipated folded conformations of peptides 1 and 2 are established by the delineation of intramolecularly hydrogen bonded NH groups and by the observation of specific cross strand NOEs. The observation of ring current shifted aromatic protons is a diagnostic of close approach of the Phe2 and Phe7 side chains. Specific assignment of aromatic proton resonances using HSQC and HSQC-TOCSY methods allow an analysis of interproton NOEs between the spatially proximate aromatic rings. This approach facilitates specific assignments in systems containing multiple aromatic rings in spectra at natural abundance. Evidence is presented for a dynamic process which invokes a correlated conformational change about the C-alpha-C-beta(chi(1)) bond for the pair of interacting Phe residues. NMR results suggest that aromatic ring orientations observed in crystals are maintained in solution. Anomalous temperature dependence of ring current induced proton chemical shifts suggests that solvophobic effects may facilitate aromatic ring clustering in apolar solvents.

Unusual Salt-Induced Color Modulation through Aggregation-Induced Emission Switching of a Bis-cationic Phenylenedivinylene-Based pi Hydrogelator

The synthesis, hydrogelation, and aggregation-induced emission switching of the phenylenedivinylene bis-N-octyl pyridinium salt is described. Hydrogelation occurs as a consequence of pi-stacking, van der Waals, and electrostatic interactions that lead to a high gel melting temperature and significant mechanical properties at a very low weight percentage of the gelator. A morphology transition from fiber-to-coil-to-tube was observed depending on the concentration of the gelator. Variation in the added salt type, salt concentrations, or temperature profoundly influenced the order of aggregation of the gelator molecules in aqueous solution. Formation of a novel chromophore assembly in this way leads to an aggregation-induced switch of the emission colors. The emission color switches from sky blue to white to orange depending upon the extent of aggregation through mere addition of external inorganic salts. Remarkably, the salt effect on the assembly of such cationic phenylenedivinylenes in water follow the behavior predicted from the well-known Hofmeister effects. Mechanistic insights for these aggregation processes were obtained through the counterion exchange studies. The aggregation-induced emission switching that leads to a room-temperature white-light emission from a single chromophore in a single solvent (water) is highly promising for optoelectronic applications.

Spatial Modulation and Space Shift Keying in Single Carrier Communication

Spatial modulation (SM) and space shift keying (SSK) are relatively new modulation techniques which are attractive in multi-antenna communications. Single carrier (SC) systems can avoid the peak-to-average power ratio (PAPR) problem encountered in multicarrier systems. In this paper, we study SM and SSK signaling in cyclic-prefixed SC (CPSC) systems on MIMO-ISI channels. We present a diversity analysis of MIMO-CPSC systems under SSK and SM signaling. Our analysis shows that the diversity order achieved by (n(t), n(r)) SSK scheme and (n(t), n(r), Theta(M)) SM scheme in MIMO-CPSC systems under maximum-likelihood (ML) detection is n(r), where n(t), n(r) denote the number of transmit and receive antennas and Theta(M) denotes the modulation alphabet of size M. Bit error rate (BER) simulation results validate this predicted diversity order. Simulation results also show that MIMO-CPSC with SM and SSK achieves much better performance than MIMO-OFDM with SM and SSK.

Formulation development and evaluation of lamivudine controlled release tablets using cross-linked sago starch

Objectives: Modified starches based polymeric substances find utmost applicability in pharmaceutical formulation development. Cross-linked starches showed very promising results in drug delivery application. The present investigation concerns with the development of controlled release tablets of lamivudine using cross-linked sago starch. Methods: The cross-linked derivative was synthesized with phosphorous oxychloride and native sago starch in basic pH medium. The cross-linked sago starch was tested for acute toxicity and drug-excipient compatibility study. The formulated tablets were evaluated for various physical characteristics, in vitro dissolution release study and in vivo pharmacokinetic study in rabbit model. Results: In vitro release study showed that the optimized formulation exhibited highest correlation (R) in case of zero order kinetic model and the release mechanism followed a combination of diffusion and erosion process. There was a significant difference in the pharmacokinetic parameters (T-max, C-max, AUC, V-d, T-1/2, and MDT) of the optimized formulation as compared to the marketed conventional tablet Lamivir (R). Conclusion: The cross-linked starch showed promising results in terms of controlling the release behavior of the active drug from the matrix. The hydrophilic matrix synthesized by cross-linking could be used with a variety of active pharmaceutical ingredients for making their controlled/sustained release formulations.

Biocides - resistance, cross-resistance mechanisms and assessment

Importance of the field: Antibiotic resistance in bacterial pathogens has increased worldwide leading to treatment failures. Concerns have been raised about the use of biocides as a contributing factor to the risk of antimicrobial resistance (AMR) development. In vitro studies demonstrating increase in resistance have often been cited as evidence for increased risks. It is therefore important to understand the mechanisms of resistance employed by bacteria toward biocides used in consumer products and their potential to impart cross-resistance to therapeutic antibiotics. Areas covered: In this review, the mechanisms of resistance and cross-resistance reported in the literature toward biocides commonly used in consumer products are summarized. The physiological and molecular techniques used in describing and examining these mechanisms are reviewed and application of these techniques for systematic assessment of biocides for their potential to develop resistance and/or cross-resistance is discussed. Expert opinion: The guidelines in the usage of biocides in household or industrial purpose should be monitored and regulated to avoid the emergence of any MDR strains. The genetic and molecular methods to monitor the resistance development to biocides should be developed and included in preclinical and clinical studies.

Performance analysis of fixed gain amplify-and-forward relaying with time-efficient cascaded channel estimation

In a cooperative system with an amplify-and-forward relay, the cascaded channel training protocol enables the destination to estimate the source-destination channel gain and the product of the source-relay (SR) and relay-destination (RD) channel gains using only two pilot transmissions from the source. Notably, the destination does not require a separate estimate of the SR channel. We develop a new expression for the symbol error probability (SEP) of AF relaying when imperfect channel state information (CSI) is acquired using the above training protocol. A tight SEP upper bound is also derived; it shows that full diversity is achieved, albeit at a high signal-to-noise ratio (SNR). Our analysis uses fewer simplifying assumptions, and leads to expressions that are accurate even at low SNRs and are different from those in the literature. For instance, it does not approximate the estimate of the product of SR and RD channel gains by the product of the estimates of the SR and RD channel gains. We show that cascaded channel estimation often outperforms a channel estimation protocol that incurs a greater training overhead by forwarding a quantized estimate of the SR channel gain to the destination. The extent of pilot power boosting, if allowed, that is required to improve performance is also quantified.

Multiuser detection in large-dimension multicode MIMO-CDMA systems with higher-order modulation

In this paper, we are interested in high spectral efficiency multicode CDMA systems with large number of users employing single/multiple transmit antennas and higher-order modulation. In particular, we consider a local neighborhood search based multiuser detection algorithm which offers very good performance and complexity, suited for systems with large number of users employing M-QAM/M-PSK. We apply the algorithm on the chip matched filter output vector. We demonstrate near-single user (SU) performance of the algorithm in CDMA systems with large number of users using 4-QAM/16-QAM/64-QAM/8-PSK on AWGN, frequency-flat, and frequency-selective fading channels. We further show that the algorithm performs very well in multicode multiple-input multiple-output (MIMO) CDMA systems as well, outperforming other linear detectors and interference cancelers reported in the literature for such systems. The per-symbol complexity of the search algorithm is O(K2n2tn2cM), K: number of users, nt: number of transmit antennas at each user, nc: number of spreading codes multiplexed on each transmit antenna, M: modulation alphabet size, making the algorithm attractive for multiuser detection in large-dimension multicode MIMO-CDMA systems with M-QAM.

QCD mini-jets contribution to the total cross-section for pions and protons and expectations at LHC

We describe our kt-resummation model for total cross-sections and show its application to pp and ¯pp scattering. The model uses mini-jets to drive the rise of the cross-section and soft gluon resummation in the infrared region to transform the violent rise of the mini-jet cross-section into a logarithmic behaviour in agreement with the Froissart bound.

Modulation Diversity for Spatial Modulation Using Complex Interleaved Orthogonal Design

In this paper, we propose modulation diversity techniques for Spatial Modulation (SM) system using Complex Interleaved Orthogonal Design (CIOD). Specifically, we show that the standard SM scheme can achieve a transmit diversity order of two by using the CIOD meant for two transmit antenna system without incurring any additional system complexity or bandwidth requirement. Furthermore, we propose a low-complexity maximum likelihood detector for our CIOD based SM schemes by exploiting the structure of the CIOD. We show with our simulation results that the proposed schemes offer transmit diversity order of two and give a better symbol error rate performance than the conventional SM scheme.

A practical approach for cross-functional vehicle body weight optimization

The goal of optimization in vehicle design is often blurred by the myriads of requirements belonging to attributes that may not be quite related. If solutions are sought by optimizing attribute performance-related objectives separately starting with a common baseline design configuration as in a traditional design environment, it becomes an arduous task to integrate the potentially conflicting solutions into one satisfactory design. It may be thus more desirable to carry out a combined multi-disciplinary design optimization (MDO) with vehicle weight as an objective function and cross-functional attribute performance targets as constraints. For the particular case of vehicle body structure design, the initial design is likely to be arrived at taking into account styling, packaging and market-driven requirements. The problem with performing a combined cross-functional optimization is the time associated with running such CAE algorithms that can provide a single optimal solution for heterogeneous areas such as NVH and crash safety. In the present paper, a practical MDO methodology is suggested that can be applied to weight optimization of automotive body structures by specifying constraints on frequency and crash performance. Because of the reduced number of cases to be analyzed for crash safety in comparison with other MDO approaches, the present methodology can generate a single size-optimized solution without having to take recourse to empirical techniques such as response surface-based prediction of crash performance and associated successive response surface updating for convergence. An example of weight optimization of spaceframe-based BIW of an aluminum-intensive vehicle is given to illustrate the steps involved in the current optimization process.

Effects of different modes of hot cross-rolling in 7010 aluminum alloy: part I. evolution of microstructure and texture

The current study describes the evolution of microstructure and texture in an Al-Zn-Mg-Cu-Zr-based 7010 aluminum alloy during different modes of hot cross-rolling. Processing of materials involves three different types of cross-rolling. The development of texture in the one-step cross-rolled specimen can be described by a typical beta-fiber having the maximum intensity near Copper (Cu) component. However, for the multi-step cross-rolled specimens, the as-rolled texture is mainly characterized by a strong rotated-Brass (Bs) component and a very weak rotated-cube component. Subsequent heat treatment leads to sharpening of the major texture component (i.e., rotated-Bs). Furthermore, the main texture components in all the specimens appear to be significantly rotated in a complex manner away from their ideal positions because of non-symmetric deformations in the two rolling directions. Detailed microstructural study indicates that dynamic recovery is the dominant restoration mechanism operating during the hot rolling. During subsequent heat treatment, static recovery dominates, while a combination of particle-stimulated nucleation (PSN) and strain-induced grain boundary migration (SIBM) causes partial recrystallization of the grain structure. The aforementioned restoration mechanisms play an important role in the development of texture components. The textural development in the current study could be attributed to the combined effects of (a) cross-rolling and inter-pass annealing that reduce the intensity of Cu component after each successive pass, (b) recrystallization resistance of Bs-oriented grains, (c) stability of Bs texture under cross-rolling, and (d) Zener pinning by Al3Zr dispersoids.

Effects of different modes of hot cross-rolling in 7010 aluminum alloy: part II. mechanical properties anisotropy

The influence of microstructure and texture developed by different modes of hot cross-rolling on in-plane anisotropy (A (IP)) of yield strength, work hardening behavior, and anisotropy of Knoop hardness (KHN) yield locus has been investigated. The A (IP) and work hardening behavior are evaluated by tensile testing at 0 deg, 45 deg, and 90 deg to the rolling direction, while yield loci have been generated by directional KHN measurements. It has been observed that specimens especially in the peak-aged temper, in spite of having a strong, rotated Brass texture, show low A (IP). The results are discussed on the basis of Schmid factor analyses in conjunction with microstructural features, namely grain morphology and precipitation effects. For the specimen having a single-component texture, the yield strength variation as a function of orientation can be rationalized by the Schmid factor analysis of a perfectly textured material behaving as a quasi-single crystal. The work hardening behavior is significantly affected by the presence of solute in the matrix and the state of precipitation rather than texture, while yield loci derived from KHN measurements reiterate the low anisotropy of the materials. Theoretic yield loci calculated from the texture data using the visco-plastic self-consistent model and Hill's anisotropic equation are compared with that obtained experimentally.