Thermal conductivity-based hydrogen in argon detector (HAD): Design, development of instrumentation, and performance evaluation

The Hydrogen in Argon Detectors (HADs) working on the principle of thermal conductivity difference between argon (reference) and argon + H2 (sample) in the cover gas of a sodium-cooled fast breeder reactor using the Wheatstone bridge circuit. The output of HAD is very sensitive to the gas flow rate and to the variation in ambient temperature. The RMSnoise of current was brought within ±1 µA by a constant current source across the bridge. The temperature correction factor fed in the processor brought down the RMSnoise in the HAD signal within ±2.4 mV than the uncorrected one having RMSnoise of ±230 mV. The filtered noise of HAD facilitates enhancing the detection limit of HAD down to 30 ppm (3σ) of hydrogen in argon.

Contact angle measurement system with liquid sodium in inert atmosphere

Liquid sodium is the heat transport medium in fast breeder reactors due to its favorable chemical, physical, and nuclear properties. Wetting of liquid sodium with the material of reactor components is essential for the effective functioning of the reactor. Liquid sodium wetting plays a crucial role, such as in (i) heat transfer and (ii) image reconstruction under sodium ultrasonic scanners. Contact angle is the inverse measure of the wetting of liquids over solid surfaces. A contact angle measurement system was set up in an inert atmosphere glow box to study the wetting behavior of liquid sodium on reactor materials. The contact angle of liquid sodium on nickel surface was measured as a function of temperature, and the results obtained were found to be in good agreement with the literature values. The contact angle of liquid sodium on SS316LN as a function of temperature was measured for the first time using this facility.

Design, development, and instrumentation of isopiestic experimental setup

An isopiestic experimental facility for the measurement of vapor pressures has been designed, fabricated, and commissioned. Using the vapor pressure data as a function of temperature, useful thermodynamic properties of alloys and compounds of interest can be derived. The isopiestic facility comprises a pair of furnaces, temperature controllers, thermocouple movement mechanism, user interface, and data collection. Four such experimental setups have been commissioned. This experimental facility is useful to determine the vapor pressures of a volatile component over the condensed phases as a function of temperature and composition. Using the vapor pressure data, the thermodynamic properties of various systems can be determined. The experimental setup was validated by a Pr-Cd isopiestic run, and the results are compared with the data reported in the literature.

Design and development of heater control circuit without temperature sensor for monitoring hydrogen in argon

A thin film based tin oxide sensor is developed to monitor low levels of hydrogen (concentration ranging from 5 to 75 ppm) in the cover gas plenum of the fast breeder test reactor. The heater and the sensor patterns are integrated on a miniature alumina substrate, and necessary electrical leads are incorporated into it. For proper functioning of the sensor, the heater has to be maintained at a constant temperature of 350 °C. This paper gives an outline of the electronics developed to measure the sensor signal and to control the heater temperature. The major challenge in this work is that there was no provision for embedding a temperature sensor on the heater surface due to physical constraints. This constrained the maintenance of a constant heater temperature for the proper functioning of the sensor. This led us to develop and demonstrate a heater control circuit without a temperature sensor to maintain a fixed temperature for monitoring hydrogen in argon, and electronics for the above-mentioned circuitry is discussed.

Design and development of instrumentation for the measurement of sensor array responses

Indigenous instrumentation has been designed and developed for the measurement of the concentration of analytes from eight conductometric metal oxide sensors. The hardware scheme of instrumentation is based on the astable multivibrator configuration. The hardware measures the resistance output from the sensors, conditions, processes, and displays the data on the liquid crystal display. An 8051 based processor averages the data, converts them into engineering units, and sends them to remote PC through ethernet communication for post-data analysis. A graphical user interface (GUI) is developed to acquire, monitor, and display the eight channels' sensor output. GUI plots the online data and offline data as a popup window. The hardware and software of the instrument were tested with standard resistors for calibration and found that in-house developed instrumentation is able to measure with an accuracy of ±0.5% with a resolution of 500 Ω. The instrument has been tested with a semiconductor metal oxide sensor, viz., chromium niobate (CrNbO₄).

Synthesis, characterization and low energy photon attenuation studies of bone tissue substitutes

Epoxy composites with different weight percentages of calcium carbonate and calcium phosphate were synthesized as bone tissue substitutes (BTS) for internal dosimetry. The Fourier-transform infrared spectroscopy analysis confirmed that no chemical reaction occurred between the polymer and the fillers. Thermogravimetric analysis also showed improvement in the thermal properties of the composites due to the fillers. The uniform distribution of fillers in the epoxy matrix was established by X-ray radiography. The attenuation behavior of BTS was probed for low energy γ source 241Am (59.5 keV) using planar HPGe detector. The measured mass attenuation coefficients of BTS were found to match with the values calculated using XCOM software. The radiological properties derived for these composites were found to be on par with those of ICRU-44 cortical bone and B-100 bone equivalent plastic.

Application of principal component analysis to gas sensing characteristics of Cr0.8Fe0.2NbO4 thick film array

The transient changes in resistances of Cr0.8Fe0.2NbO4 thick film sensors towards specified concentrations of H2, NH3, acetonitrile, acetone, alcohol, cyclohexane and petroleum gas at different operating temperatures were recorded. The analyte-specific characteristics such as slopes of the response and retrace curves, area under the curve and sensitivity deduced from the transient curve of the respective analyte gas have been used to construct a data matrix. Principal component analysis (PCA) was applied to this data and the score plot was obtained. Distinguishing one reducing gas from the other is demonstrated based on this approach, which otherwise is not possible by measuring relative changes in conductivity. This methodology is extended for three Cr0.8Fe0.2NbO4 thick film sensor array operated at different temperatures.

Advantages of collagen based biological dressings in the management of superficial and superficial partial thickness burns in children

Collagen based dressings for acute burn wound management have been extensively used in India, particularly in the city of Chennai. Due to the high levels of humidity in our city, closed dressings become infected and treatment with topical antimicrobials, like Silver Sulfadiazine cream, quickly become desiccated. Collagen membrane dressings were manufactured by the biomaterial laboratory of the Central Leather Research Institute (CLRI), Government of India in Chennai, and then the process was patented. Collagen was extracted from bovine skin and Achilles tendons, and then reconstituted. This was used on burn wounds as dressings after clearance from the Institutional Review Board and Ethics Committees of the Hospital and CLRI. Continued research in this field to enable resulted in the design of silver sulphadiazine loaded alginate microspheres which were embedded in the reconstituted collagen. Controlled delivery of silver sulphadiazine. This collagen membrane was used in chronic infected burns. Low molecular weight heparin was given subcutaneously to improve wound healing in burn injuries and collagen membrane dressings were also applied. After several trials the process technology was patented. The advantages and disadvantages of the collagen membrane cover is elaborated in a group of 487 pediatric burn patients. The trial was conducted at the burn unit of Kanchi Kamakoti Childs Trust Hospital (KKCTH) in Chennai, India.

Rapidly swept, ultra-widely-tunable 1060 nm MEMS-VCSELs

Demonstrated are 1060 nm microelectromechanical-systems-based tunable vertical-cavity surface-emitting lasers (MEMS-VCSELs) with a 100 nm continuous tuning range under repetitively scanned operation at rates beyond 500 kHz and a 90 nm continuous tuning range under static operation. These devices employ a thin strained InGaAs multiple quantum well active region integrated with a fully oxidised GaAs/Al_xO_y bottom mirror and a suspended dielectric top mirror. The devices are optically pumped via 850 nm light. These ultra-widely tunable lasers represent the first MEMS-VCSELs reported in this wavelength range, and are ideally suited for application in ophthalmic swept-source optical coherence tomography.

A challenging case of total phalloplasty

Plastic surgery continues to maintain a prominent presence in the evolution of male genital reconstruction. In this case report, we are presenting a case of post-electric burn with a total loss of penis. Sustaining other major injuries following an electric burn with loss of right upper limb and extensive tissue damage to left upper limb, abdomen and both thighs, this young male patient was initially managed from life-threatening problems. With many options closed following a major electric burn and its acute management, penile and urethral reconstruction was a unique and a great challenge in this patient. Heeding to the patient's wish of male pattern micturition, we had performed a successful reconstruction of urethra and entire phallus with groin flap.

High-sweep-rate 1310 nm MEMS-VCSEL with 150 nm continuous tuning range

Microelectromechanical-systems-based vertical-cavity surface-emitting lasers (MEMS-VCSELs) capable of a 150 nm continuous tuning range near 1310 nm are demonstrated. These devices employ a thin optically pumped active region structure with large free-spectral range, which promotes wide and continuous tuning. To achieve VCSEL emission at 1310 nm, a wide-gain-bandwidth indium phosphide-based multiple quantum well active region is combined with a wide-bandwidth fully oxidised GaAs-based mirror through wafer bonding, with tuning enabled by a suspended dielectric top mirror. These devices are capable of being scanned over the entire tuning range at frequencies up to 500 kHz, making them ideal for applications such as swept source optical coherence tomography and high-speed transient spectroscopy.

Current scenario in chemical burns in a developing country: Chennai, India

Chemical burns are not uncommon in India. Both accidental and non-accidental chemical burns are encountered in our setting. In the paediatric age group, chemical burns are mainly accidental. Analysis of chemical burn admissions to the Burn Units of a medical college hospital, and to an exclusively tertiary care children's hospital in Chennai, India, from 2001 to 2010 is described. A total number of 75 adults and 38 children are included in the study. Detailed analysis of age, sex, percentage of burn total body surface area (TBSA %), causative agents, aetiology (accidental or non-accidental), treatment instituted, mortality, and outcome are reported.

Profile of burn sepsis challenges and outcome in an exclusive children's hospital in Chennai, India

A group of 273 paediatric patients admitted to Kanchi Kamakoti Childs Trust Hospital Burn Unit, Chennai, India between the years 2004 to 2010 were analysed retrospectively. Of these, 89 were suffering from sepsis and septic shock and 15 died. Strict adherence to antibiotic administration and to the Paediatric Intensive Care Unit (PICU) and management protocol improved the outcome, especially in 2009 and 2010.

Glutamate receptors as seen by light: spectroscopic studies of structure-function relationships

Ionotropic glutamate receptors are major excitatory receptors in the central nervous system and also have a far reaching influence in other areas of the body. Their modular nature has allowed for the isolation of the ligand-binding domain and for subsequent structural studies using a variety of spectroscopic techniques. This review will discuss the role of specific ligand:protein interactions in mediating activation in the a-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid subtype of glutamate receptors as established by various spectroscopic investigations of the GluR2 and GluR4 subunits of this receptor. Specifically, this review will provide an introduction to the insight gained from X-ray crystallography and nuclear magnetic resonance investigations and then go on to focus on studies utilizing vibrational spectroscopy and fluorescence resonance energy transfer to study the behavior of the isolated ligand-binding domain in solution and discuss the importance of specific ligand:protein interactions in the mechanism of receptor activation.

Facially disfigured children--dedicated approach and rehabilitation

Facial disfigurement following congenital anomalies or acquired defects due to accidents or scars results in mental trauma and other related consequences. A multidisciplinary team approach with special importance to rehabilitation is required in handling such patients.

Low molecular weight heparin-induced pharmacological modulation of burn wound healing

Low molecular weight heparin (LMWH) appears to be a promising solution for reducing inflammatory post-burn episodes and results in improved healing. The clinical examination presented here includes patients with burn wounds ranging from 20 to 35% total body surface area (TBSA) who were categorized into two groups, of which one received subcutaneous LMWH treatment (10,000 units/day) and the other acted as control. The process of healing was assessed through regular examination of clinical features such as regression of erythema and oedema, eschar formation, and rate of re-epithelialization. Various studies have demonstrated an increase in levels of serum IL-6 indicating the severity of the morbid condition. In the present investigation, LMWH-treated patients exhibited a faster decline in levels of serum IL-6 (within 12 days) than control. Infiltration of inflammatory cells at the local wound site was assessed through a histological analysis of tissue samples taken on various days during the healing process. The LMWH-treated groups exhibited an organized healing pattern with better remodelling in a shorter duration (28 days), while control patients took more than 28 days for complete healing. A slight correlation was observed with TBSA to the inflammatory process, which subsided in patients treated with LMWH, favourably modulating the events involved in the inflammatory process of burn wound healing.

Ultrastructural differentiation of abnormal scars

AIM

To evaluate the differences between keloid and hypertrophic scars by biochemical and ultrastructural techniques.

METHOD

Over 1000 patients with different types of scars were studied and followed up for a period of 20 years. The histochemical and biochemical analysis with respect to the composition of the extracellular matrix of the dermis was conducted. At the ultrastructural level, collagen deposition and assembly were studied using electron microscopy. The rate of proliferation and metabolic activity of the dermal fibroblasts isolated from the normal skin and scar biopsies were studied to assess the cause of excess matrix deposition in scar tissues.

RESULTS

Evaluation of different types of scars showed that both keloid and hypertrophic scars have excess matrix deposition in terms of collagen and proteoglycans. Keloid shows a high amount of acid-soluble collagen. The assembly of collagen fibrils is also abnormal in keloids. Studies on the proliferation and metabolic activity showed that keloid fibroblasts have a higher rate of proliferation and metabolic activity than fibroblasts from hypertrophic scars and normal skin. Finally, keloid fibroblasts show high and intense staining for the endoplasmic reticulum, suggesting a possible reason for high activity of these fibroblasts.

CONCLUSION

Keloids and hypertrophic scars show distinct ultrastructural patterns of both collagen deposition and assembly. These parameters could be refined by further research, and they would thus serve as a useful tool for surgeons to distinguish different types of scars and adopt suitable therapeutic strategies.

Paediatric rehabilitation in a developing country--India in relation to aetiology, consequences and outcome in a group of 459 burnt children

Age, aetiology of burn, percentage body surface area burnt and post-burn sequelae have a direct relationship to the rehabilitative necessity in burnt children in a developing country--India. In spite of the gross disfigurements and sequelae, only adolescent children required psychosocial rehabilitation. These are the results following a retrospective analysis of 459 paediatric burn patients in Madras, India.

Ultrasound-assisted fabrication of nanoporous CdS films

A new method for fabricating nanoporous CdS films is reported. It involves exposing the CdS solution with ultrasound waves during the process of dip coating. Indium tin oxide (ITO)-coated glass and plastic (commercial transparency) were used as substrates. In each case three different precursors were used for dip coating. The precursors used were CdCl2 and thiourea in one case and CdS nanoparticles prepared by sonochemical and microwave-assisted methods in the other two cases. X-ray diffraction studies performed on these powders show a phase corresponding to cubic CdS. The Field Emission Scanning Electron Microscopy (FE-SEM) images of the films on plastic showed uniform pores with a diameter of 80 nm for all three methods. Optical absorption measurements indicated a blue shift and multiple peaks in the absorption curve. The FE-SEM observations of the films on an ITO/glass substrate indicated a crystalline film with voids. The UV-vis absorption results indicated a blue shift in the absorption with an absorption edge at 435, 380, and 365 nm for CdS films made by solution growth, sonochemical, and microwave routes, respectively. The magnitude of the absorption is dependent on film thickness, and the observed blue shift in the absorption can be explained on the basis of quantum confinement effects.

Effect of trypsin-chymotrypsin (Chymoral Forte D.S.) preparation on the modulation of cytokine levels in burn patients

The present study was carried out in burn patients administered with Trypsin-Chymotrypsin (Chymoral Forte D.S.) preparation to observe if the acute-phase protein levels in the serum are modulated through the synthesis of IL-1beta and IL-6 and if the severity of the inflammatory phase could be regulated. The effects of Trypsin-Chymotrypsin preparation on the modulation of cytokine levels particularly, IL-6 and IL-1beta were analyzed in serum samples of 15 burn patients and compared with untreated controls. Significant differences in cytokine levels (P<0.05) were observed in untreated burn patients and Trypsin-Chymotrypsin preparation treated patients. There were significant variations in serum IL-6 and IL-1beta on the day of admission and post burn day 10 in treated as well as untreated burn patients. Patients with a higher percentage of total body surface area and sepsis showed a significant increase in IL-1beta and IL-6 in the serum. An increase in serum levels of both cytokines was observed on post burn day 1 and a significant decrease was observed in Trypsin-Chymotrypsin preparation treated patients on days 7 and 10. The possible role of the inflammatory cytokines in the pathophysiology of burns is discussed.

Stereochemistry of quinoxaline antagonist binding to a glutamate receptor investigated by Fourier transform infrared spectroscopy

The stereochemistry of the interactions between quinoxaline antagonists and the ligand-binding domain of the glutamate receptor 4 (GluR4) have been investigated by probing their vibrational modes using Fourier transform infrared spectroscopy. In solution, the electron-withdrawing nitro groups of both compounds establish a resonance equilibrium that appears to stabilize the keto form of one of the cyclic amide carbonyl bonds. Changes in the 6,7-dinitro-2,3-dihydroxyquinoxaline vibrational spectra on binding to the glutamate receptor, interpreted within the framework of a published crystal structure, illuminate the stereochemistry of the interaction and suggest that the binding site imposes a more polarized electronic bonding configuration on this antagonist. Similar spectral changes are observed for 6-cyano-7-dinitro-2,3-dihydroxyquinoxaline, confirming that its interactions with the binding site are highly similar to those of 6,7-dinitro-2,3-dihydroxyquinoxaline and leading to a model of the 6-cyano-7-dinitro-2,3-dihydroxyquinoxaline-S1S2 complex, for which no crystal structure is available. Conformational changes within the GluR ligand binding domain were also monitored. Compared with the previously reported spectral changes seen on binding of the agonist glutamate, only a relatively small change is detected on antagonist binding. This correlation between the functional effects of different classes of ligand and the magnitude of the spectroscopic changes they induce suggests that the spectral data reflect physiologically relevant conformational processes.

Mechanism-based discovery of ligands that counteract inhibition of the nicotinic acetylcholine receptor by cocaine and MK-801

Nicotinic acetylcholine receptors (AChR) belong to a family of proteins that form ligand-gated transmembrane ion channels. They are involved in the fast transmission of signals between cells and the control of intercellular communication in the nervous system. A variety of therapeutic agents and abused drugs, including cocaine, inhibit the AChR and monoamine transporters and interfere with nervous system function. Here we describe a mechanism-based approach to prevent this inhibition. We had previously developed presteady-state kinetic (transient kinetic) techniques, with microsecond-to-millisecond time resolutions, for investigations of reactions on cell surfaces that allow one to determine the effects of inhibitors not only on the channel-opening probability but also on the opening and closing rates of the AChR channel. The transient kinetic measurements led to two predictions. (i) Ligands that bind to a regulatory site on the closed-channel conformation of the AChR with higher affinity than to the site on the open-channel form shift the equilibrium toward the closed-channel form, thereby inhibiting the receptor. (ii) Ligands that bind to a regulatory site with an affinity for the open conformation equal to or higher than their affinity for the closed conformations are expected not to inhibit the receptor and to displace inhibitors. The identification of such ligands in a combinatorial library of RNA ligands is reported. The implication of this approach to other protein-mediated reactions in which an inhibitor changes the equilibrium between active and inactive conformations is discussed.

Ligand--protein interactions in the glutamate receptor

Fourier transform infrared spectroscopy was used to investigate ligand-protein interactions in the ligand-binding domain of the GluR4 glutamate receptor subunit. Glutamate binding induces more extensive secondary structural changes in the ligand-binding domain than does kainate binding. Glutamate also alters the hydrogen bonding strength of the single free cysteine side chain in the domain, while kainate does not. On the other hand, the interaction of a binding site arginine residue with kainate appears to be stronger than that with glutamate. These results identify chemical and structural differences that may explain the different functional characteristics of the two agonists acting on ionotropic glutamate receptors. In doing so, they complement and extend recent crystallographic structures of the ligand-binding domain.