Physical insights into salicylic acid release from poly(anhydrides)

Salicylic acid (SA) based biodegradable polyanhydrides (PAHs) are of great interest for drug delivery in a variety of diseases and disorders owing to the multi-utility of SA. There is a need for the design of SA-based PAHs for tunable drug release, optimized for the treatment of different diseases. In this study, we devised a simple strategy for tuning the release properties and erosion kinetics of a family of PAHs. PAHs incorporating SA were derived from related aliphatic diacids, varying only in the chain length, and prepared by simple melt condensation polymerization. Upon hydrolysis induced erosion, the polymer degrades into cytocompatible products, including the incorporated bioactive SA and diacid. The degradation follows first order kinetics with the rate constant varying by nearly 25 times between the PAH obtained with adipic acid and that with dodecanedioic acid. The release profiles have been tailored from 100% to 50% SA release in 7 days across the different PAHs. The release rate constants of these semi-crystalline, surface eroding PAHs decreased almost linearly with an increase in the diacid chain length, and varied by nearly 40 times between adipic acid and dodecanedioic acid PAH. The degradation products with SA concentration in the range of 30-350 ppm were used to assess cytocompatibility and showed no cytotoxicity to HeLa cells. This particular strategy is expected to (a) enable synthesis of application specific PAHs with tunable erosion and release profiles; (b) encompass a large number of drugs that may be incorporated into the PAH matrix. Such a strategy can potentially be extended to the controlled release of other drugs that may be incorporated into the PAH backbone and has important implications for the rational design of drug eluting bioactive polymers.

Ionothermal Synthesis of High-Voltage Alluaudite Na2+2xFe2-x(SO4)(3) Sodium Insertion Compound: Structural, Electronic, and Magnetic Insights

Exploring future cathode materials for sodium-ion batteries, alluaudite class of Na2Fe2II(SO4)(3) has been recently unveiled as a 3.8 V positive insertion candidate (Barpanda et al. Nat. Commun. 2014, 5, 4358). It forms an Fe-based polyanionic compound delivering the highest Fe-redox potential along with excellent rate kinetics and reversibility. However, like all known SO4-based insertion materials, its synthesis is cumbersome that warrants careful processing avoiding any aqueous exposure. Here, an alternate low temperature ionothermal synthesis has been described to produce the alluaudite Na2+2xFe2-xII(SO4)(3). It marks the first demonstration of solvothermal synthesis of alluaudite Na2+2xM2-xII(SO4)(3) (M = 3d metals) family of cathodes. Unlike classical solid-state route, this solvothermal route favors sustainable synthesis of homogeneous nanostructured alluaudite products at only 300 degrees C, the lowest temperature value until date. The current work reports the synthetic aspects of pristine and modified ionothermal synthesis of Na2+2xFe2-xII(SO4)(3) having tunable size (300 nm similar to 5 mu m) and morphology. It shows antiferromagnetic ordering below 12 K. A reversible capacity in excess of 80 mAh/g was obtained with good rate kinetics and cycling stability over 50 cycles. Using a synergistic approach combining experimental and ab initio DFT analysis, the structural, magnetic, electronic, and electrochemical properties and the structural limitation to extract full capacity have been described.

Critical investigation of high performance spin-coated high-kappa titania thin films based MOS capacitor

We report the tunable dielectric constant of titania films with low leakage current density. Titanium dioxide (TiO2) films of three different thicknesses (36, 63 and 91 nm) were deposited by the consecutive steps of solution preparation, spin-coating, drying, and firing at different temperatures. The problem of poor adhesion between Si substrate and TiO2 insulating layer was resolved by using the plasma activation process. The surface roughness was found to increase with increasing thickness and annealing temperature. The electrical investigation was carried out using metal-oxide-semiconductor structure. The flat band voltage (V-FB), oxide trapped charge (Q(ot)), dielectric constant (kappa) and equivalent oxide thicknesses are calculated from capacitance-voltage (C-V) curves. The C-V characteristics indicate a thickness dependent dielectric constant. The dielectric constant increases from 31 to 78 as thickness increases from 36 to 91 nm. In addition to that the dielectric constant was found to be annealing temperature and frequency dependent. The films having thickness 91 nm and annealed at 600 A degrees C shows the low leakage current density. Our study provides a broad insight of the processing parameters towards the use of titania as high-kappa insulating layer, which might be useful in Si and polymer based flexible devices.

Experimental Investigations on the Pulsed Power Switch of a HIRA based UWB System

The Ultra Wide Band (UWB) system has been a subject of research in the last few years due to its utility in various high power electromagnetic applications. Due to its simplicity in design and fabrication, the Half Impulse Radiating Antenna (HIRA) based UWB system has attracted many researchers. Effectiveness of a UWB system, in terms of the bandwidth of the radiated pulse depends on the duration of the radiated field which is typically of sub nanosecond regime. This duration in turn depends on the closure time of the switch used in the UWB pulsed power source. This paper presents the work carried out on the pressurised gas switch of a 50 kV pulsed power system of a HIRA based UWB system. The aim of the present work is to establish the relationship between the pulser switch breakdown voltage and gas pressure, rise time and gas pressure as well as the dependency of the Pulse Repetition Rate (PRR) on the switch breakdown voltage.

Reduction Approaches for Vibration Control of Repetitive Structures

The reduction approaches are presented for vibration control of symmetric, cyclic periodic and linking structures. The condensation of generalized coordinates, the locations of sensors and actuators, and the relation between system inputs and control forces are assumed to be set in a symmetric way so that the control system posses the same repetition as the structure considered. By employing proper transformations of condensed generalized coordinates and the system inputs, the vibration control of an entire system can be implemented by carrying out the control of a number of sub-structures, and thus the dimension of the control problem can be significantly reduced.

Colliding-pulse modelocked quantum dot lasers

Colliding pulse modelocking is demonstrated for the first time in quantum dot lasers. Using 3.9 mm-long devices with a 245 pm-long central absorber, 7 ps pulses at a repetition rate of 20 GHz is obtained. For Gaussian pulses a time-bandwidth product close to the Fourier transform limit is determined. These results confirm the potential of quantum dot lasers for high repetition rate harmonic modelocking.

Laser drilling improving circuit board manufacturing

We reported here a novel technique for laser high speed drillings on Printed Circuit Boards (PCBs). A CNC solid laser based system is developed to drill through and blind vias as an alternative to mechanical drilling. The system employs an Acousto-Optic Q-switched Nd: YAG laser, a computer control system and an X-Y moving table which can handle up to 400 x 400 mm PCB. With a special designed cavity the laser system works in a pulsed operation in order to generate pulses with width down to 0.5 mu s and maximum peak power over 10kW at 10k repetition rate. Delivered by an improved optical beam transforming system, the focused laser beam can drill hobs including blind vias on PCBs with diameter in the range of 0.1 - 0.4 mm and at up to 300 - 500 vias per second (depending on the construction of PCBs). By means of a CNC X-Y moving system, laser pulses with pulse-to-pulse superior repeatability can be fired at desired location on a PCBs with high accuracy. This alternative technology for drilling through or blind vias on PCBs or PWBs (printed wiring boards) will obviously enhance the capability to printed boards manufacturing.

Broad spectrum measurement of the birefringence of an isothiocyanate based liquid crystal.

Tunable materials with high anisotropy of refractive index and low loss are of particular interest in the microwave and terahertz range. Nematic liquid crystals are highly sensitive to electric and magnetic fields and may be designed to have particularly high birefringence. In this paper we investigate birefringence and absorption losses in an isothiocyanate based liquid crystal (designed for high anisotropy) in a broad range of the electromagnetic spectrum, namely 0.1-4 GHz, 30 GHz, 0.5-1.8 THz, and in the visible and near-infrared region (400 nm-1600 nm). We report high birefringence (Δn = 0.19-0.395) and low loss in this material. This is attractive for tunable microwave and terahertz device applications.

Uncooled DBR laser directly modulated at 3.125 Gb/s as athermal transmitter for low-cost WDM systems

An uncooled three-section tunable distributed Bragg reflector laser is demonstrated as an athermal transmitter for low-cost uncooled wavelength-division-multiplexing (WDM) systems with tight channel spacing. A ±0.02-nm thermal wavelength drift is achieved under continuous-wave operation up to 70 °C. Dynamic sidemode suppression ratio of greater than 35 dB is consistently obtained under 3.125-Gb/s direct modulation over a 20 °C-70 °C temperature range, with wavelength variation of as low as ±0.2 nm. This indicates that more than an order of magnitude reduction in coarse WDM channel spacing is possible using this source. © 2005 IEEE.

Characterisation of ultrafast micro-structuring of alumina (Al 2O3)

Alumina ceramic, Al2O3, presents a challenge to laser micro-structuring due to its neglible linear absorption coefficient in the optical region coupled with its physical properties such as extremely high melting point and high thermal conductivity. In this work, we demonstrate clean micro-structuring of alumina using NIR (λ=775 nm) ultrafast optical pulses with 180 fs duration at 1kHz repetition rate. Sub-picosecond pulses can minimise thermal effects along with collateral damage when processing conditions are optimised, consequently, observed edge quality is excellent in this regime. We present results of changing micro-structure and morphology during ultrafast processing along with measured ablation rates and characteristics of developing surface relief. Initial crystalline phase (alpha Al2O3) is unaltered by femtosecond processing. Multi-pulse ablation threshold fluence Fth, ∼ 1.1 Jcm-2 and at low fluence ∼ 3 Jcm -2, independent of machined depth, there appears to remain a ∼ 2 μm thick rapidly re-melted layer. On the other hand, micro-structuring at high fluence F ∼ 21 Jcm-2 shows no evidence of melting and the machined surface is covered with a fine layer of debris, loosely attached. The nature of debris produced by femtosecond ablation has been investigated and consists mainly of alumina nanoparticles with diameters from 20 nm to 1 micron with average diameter ∼ 300 nm. Electron diffraction shows these particles to be essentially single crystal in nature. By developing a holographic technique, we have demonstrated periodic micrometer level structuring on polished samples of this extremely hard material.

Curvature and wrinkling of premixed flame Kernels comparison between planar laser induced fluorescence (PLIF) and 3D direct numerical simulations (DNS)

A direct comparison between time resolved PLIF measurements of OH and two dimensional slices from a full three dimensional DNS data set of turbulent premixed flame kernels in lean methane/air mixture was presented. The local flame structure and the degree of flame wrinkling were examined in response to differing turbulence intensities and turbulent Reynolds numbers. Simulations were performed using the SEGA DNS code, which is based on the solution of the compressible Navier Stokes, species, and energy equations for a lean hydrocarbon mixture. For the OH PLIF measurements, a cluster of four Nd:YAG laser was fired sequentially at high repetition rates and used to pump a dye laser. The frequency doubled laser beam was formed into a sheet of 40 mm height using a cylindrical telescope. The combination of PLIF and DNS has been demonstrated as a powerful tool for flame analysis. This research will form the basis for the development of sub-grid-scale (SGS) models for LES of lean-premixed combustion systems such as gas turbines. This is an abstract of a paper presented at the 30th International Symposium on Combustion (Chicago, IL 7/25-30/2004).

Parentesco, prestigio y poder en la alta edad media : la antroponimia aristocrática en el Reino de León (siglos X y XI)

Resumen: El presente trabajo analiza la antroponimia de la aristocracia leonesa en los siglos X y XI, a fi n de contribuir a la comprensión de las estructuras de parentesco de los grupos aristocráticos, las manifestaciones de la memoria familiar y el papel del parentesco en la construcción del poder y el prestigio social. Se plantea que la aristocracia desarrolló una antroponimia específi ca basada en la reiteración de determinados nombres propios a lo largo de las generaciones, que constituyó un importante elemento de identifi cación de la parentela y que expresó en el plano simbólico la organización de los grupos de parentesco en función de la transmisión del poder y la afi rmación del prestigio familiar.

Effects of mechanical and electrical coupling on the parametric sensitivity of mode localized sensors

We compare and contrast the effects of two distinctly different mechanisms of coupling (mechanical and electrical) on the parametric sensitivity of micromechanical sensors utilizing mode localization for sensor applications. For the first time, the strong correlation between mode localization and the phenomenon of 'eigenvalue loci-veering' is exploited for accurate quantification of the strength of internal coupling in mode localized sensors. The effects of capacitive coupling-spring tuning on the parametric sensitivity of electrically coupled resonators utilizing this sensing paradigm is also investigated and a mass sensor with sensitivity tunable by over 400% is realized. ©2009 IEEE.

Rendimiento y calidad de las interacciones sociocognitivas en díadas que trabajan colaborativamente en forma presencial y por chat

Resumen: En este trabajo se examina el rendimiento de estudiantes universitarios en razonamiento formal con y sin interacción social. La muestra N = 83 estuvo conformada por alumnos provenientes de dos universidades (UNMDP y UAA) quienes fueron asignados a dos condiciones: experimental con interacción (n = 40) y grupo control sin interacción (n = 43). El reactivo empleado consistió en una serie de pruebas del Test de Matrices Progresivas escala general y avanzada. Todos los participantes debieron resolver dichas tareas durante varias semanas: primero en forma individual (pretest), luego en forma colectiva presencial y por chat (díadas, condición experimental) y en forma individual (grupo control), y finalmente en forma individual (postest). Se registraron las interacciones que llevaron a cabo los participantes mediante videofilmación y logs del Chat. El rendimiento fue evaluado según la condición asignada: individual o grupal y en los últimos mediante una evaluación interjueces se estableció la calidad de las interacciones. Los resultados corroboran la superioridad de las díadas por sobre la performance individual; la reiteración en la fase de postest de aquellos ítems incorrectamente resueltos en el pretest más el agregado de nuevos ejercicios pusieron de relieve dos zonas de avance o de internalización de los progresos. En cuanto a la calidad de las interacciones, las mismas son coincidentes. Estos resultados abren nuevos interrogantes acerca del conflicto sociocognitivo y su papel para el avance grupal – individual.

High peak power femtosecond pulse VECSELs for terahertz time domain spectroscopy

We report on a high peak power femtosecond modelocked VECSEL and its application as a drive laser for an all semiconductor terahertz time domain spectrometer. The VECSEL produced near-transform-limited 335 fs sech2 pulses at a fundamental repetition rate of 1 GHz, a centre wavelength of 999 nm and an average output power of 120 mW. We report on the effect that this high peak power and short pulse duration has on our generated THz signal.