Room temperature ammonia sensing using tapered multimode fiber coated with polyaniline nanofibers

We demonstrate an ammonia sensor composed of a tapered multimode fiber coated with polyaniline nanofibers that operates at room temperature (26°C). The optical properties of the polyaniline layer changes when it is exposed to ammonia, leading to a change in the absorption of evanescent field. The fiber sensor was tested by exposing it to ammonia at different concentrations and the absorbance is measured using a spectrophotometer system. Measured response and recovery times are about 2.27 minutes and 9.73 minutes, respectively. The sensor sensitivity can be controlled by adjusting the tapered fiber diameter and the highest sensitivity is achieved when the diameter is reduced to 20 µm.

Microbial biotransformation: a tool for drug designing (Review)

For centuries microbial biotransformation has proved to be an imperative tool in alleviating the production of various chemicals used in food, pharmaceutical, agrochemical and other industries. In the field of phar- maceutical research and development, biotransformation studies have been extensively applied to investigate the metabolism of compounds (leads, lead candidates, etc.) using animal models. The microbial biotransfor- mation phenomenon is then commonly employed in comparing metabolic pathways of drugs and scaling up the metabolites of interest discovered in these animal models for further pharmacological and toxicological evaluation. Microorganisms can conveniently afford drugs difficult obtained via synthesis. The plethora of reported microbial biotransformations along with its added benefits has already invoked further research in bioconversion of novel and structurally complex drugs. This review alternatively discusses the prospect of microbial biotransformation studies as a significant element ameliorating drug discovery and design in terms of cost-effectiveness, environment protection and greater structural diversity as compared to animal models used to study metabolism. To explicate the microbial biotransformation paradigm in drug designing 3 main areas in this aspect have been analyzed: 1--lead expansion: obtaining pharmacologically improved metabo- lites from bioactive molecules; 2--biosynthesis of precursors/intermediates involved in the production of bioactive molecules; 3--resolution of racemic mixture to obtain enantiomers possessing different pharma- cological profiles.

Generation and transmission of 3 × 3 W-Band multi-input multi-output orthogonal frequency division multiplexing-radio-over-fiber signals using micro-ring resonators

Using the micro-ring resonator (MRR) system, the single and multi-carriers at frequencies of f(1)=192.898, f(2)=192.990, f(3)=193.1, f(4)=193.315, and f(5)=193.537  THz with a free spectral range (FSR) of 92, 110, 215, and 222 GHz, respectively, are generated to be suitable for a radio-over-fiber (RoF) system based on multi-input multi-output (MIMO) with orthogonal frequency division multiplexing (OFDM). Demonstrated are the concepts of all-optical MIMO signal generation and its transmission over a 50 km single mode fiber (SMF) optical link and an up to 3 m wireless link. Sixty-four multi-carriers are used in the all-optical generation of three MIMO W-Band RF signals, where the single carriers (f(3)-f(5)) transport the signals over the RoF link. The bit error rate (BER) of the overall system performance is discussed; thus, the transmission of MIMO signals is feasible for up to an SMF path 50 km long and a wireless distance of 3 m.

Multiwall carbon nanotube polyvinyl alcohol-based saturable absorber in passively Q-switched fiber laser

In this work, we demonstrated a compact Q-switched erbium-doped fiber laser capable of generating high-energy pulses using a newly developed multiwall carbon nanotube (CNT) polyvinyl alcohol (PVA) thin film based saturable absorber. Q-switched pulse operation is obtained by sandwiching the thin film between two fiber ferrules forming a saturable absorber. A saturable absorber with 1.25 wt. % of PVA concentration shows a consistency in generating pulsed laser with a good range of tunable repetition rate, shortest pulse width, and produces a high pulse energy and peak power. The pulse train generated has a maximum repetition rate of 29.9 kHz with a corresponding pulse width of 3.49 μs as a function of maximum pump power of 32.15 mW. The maximum average output power of the Q-switched fiber laser system is 1.49 mW, which translates to a pulse energy of 49.8 nJ. The proposed method of multiwall CNT/PVA thin film fabrication is low in cost and involves uncomplicated processes.

Tunable single Stokes extraction from 20 GHz Brillouin fiber laser using ultranarrow bandwidth optical filter

The individual extraction of a Brillouin Stokes line from a 20 GHz comb generated from the compact configuration of a multiwavelength Brillouin fiber ring laser configuration has been achieved using an ultranarrow bandwidth (UNB) optical filter. The narrowest bandwidth transmission of a UNB optical filter that is 50 pm is used in order to get particular Stokes. The Stokes filtered is in the wavelength range of 1549.768-1551.016 nm. High SNR within the range of 54.97-11.73 dB with almost nil peak power loss being obtained was monitored by a 0.16 pm optical spectrum analyzer, giving convincing results. Relatively, the proposed configuration could provide wide tunability and narrow selection of the Brillouin Stokes.

Closely spaced dual-wavelength fiber laser using an ultranarrow bandwidth optical filter for low radio frequency generation

A dual-wavelength (DW) fiber laser with a closely spaced single longitudinal mode (SLM) output is proposed and demonstrated. The proposed fiber laser utilizes a conventional fiber Bragg grating with a center wavelength of about 1546.8 nm in conjunction with an ultranarrow bandwidth tunable optical filter to generate the desired DW SLM output. Observations with a very high resolution optical spectrum analyzer, which was capable of achieving resolutions up to 0.16 pm, revealed detailed spectral characteristics not characteristically seen before. A channel spacing of up to 58 nm was realized, and spacing as small as 2 pm was achieved. The minimum channel spacing and its resulting beat frequency are the narrowest observed yet to the best of our knowledge for a DW fiber laser at room temperature.

An insight into structure and stability of DNA in ionic liquids from molecular dynamics simulation and experimental studies

Molecular dynamics simulation and biophysical analysis were employed to reveal the characteristics and the influence of ionic liquids (ILs) on the structural properties of DNA. Both computational and experimental evidence indicate that DNA retains its native B-conformation in ILs. Simulation data show that the hydration shells around the DNA phosphate group were the main criteria for DNA stabilization in this ionic media. Stronger hydration shells reduce the binding ability of ILs' cations to the DNA phosphate group, thus destabilizing the DNA. The simulation results also indicated that the DNA structure maintains its duplex conformation when solvated by ILs at different temperatures up to 373.15 K. The result further suggests that the thermal stability of DNA at high temperatures is related to the solvent thermodynamics, especially entropy and enthalpy of water. All the molecular simulation results were consistent with the experimental findings. The understanding of the properties of IL-DNA could be used as a basis for future development of specific ILs for nucleic acid technology.

Photonic crystal fiber based dual-wavelength Q-switched fiber laser using graphene oxide as a saturable absorber

A Q-switched dual-wavelength fiber laser with narrow channel spacing is proposed and demonstrated. The fiber laser is built around a 3 m long erbium doped fiber as the gain medium and a 10 cm long photonic crystal fiber (PCF) as the element used to generate the dual-wavelength output. The PCF has a solid core approximately 4.37 μm in diameter and is surrounded by microscopic air-holes with a diameter of about 5.06 μm each as well as a zero-dispersion wavelength of about 980 nm. A graphene oxide based saturable absorber is used to generate the desired pulsed output. At the maximum pump power of 72 mW the laser is capable of generating pulses with a repetition rate and pulse-width of 31.0 kHz and 7.0 μs, respectively, as well as an average output power and pulse energy of 0.086 mW and 2.8 nJ, respectively. The proposed fiber laser has substantial potential for use in applications that require longer duration pulsed outputs such as in range finding and terahertz radiation generation.

Graphene oxide-based waveguide polariser: from thin film to quasi-bulk

We have demonstrated a broadband waveguide polariser with high extinction ratio on a polymer optical waveguide coated with graphene oxide via the drop-casting method. The highest extinction ratio of nearly 40 dB is measured at 1590 nm, with a variation of 4.5 dB across a wavelength range from 1530 nm to 1630 nm, a ratio that is (to our knowledge) the highest reported for graphene-based waveguide polarisers to date. This result is achieved with a graphene oxide coating length along the propagation direction of only 1.3 mm and a bulk film thickness of 2.0 µm. The underlying principles of the strongly polarisation dependent propagation loss demonstrated have been studied and are attributed to the anisotropic complex dielectric function of graphene oxide bulk film.

Clostridium difficile infections in HIV-positive patients with diarrhoea

BACKGROUND

Patients with HIV/AIDS are at a high risk of being infected with toxin-producing strains of Clostridium difficile (C. difficile) because of frequent hospitalization, exposure to antibiotics and antibiotic prophylaxis for opportunistic infections. There are little data from India on the prevalence of C. difficile infection in such patients.

METHODS

We assessed the occurrence of C. difficile infections in HIV-positive patients with diarrhoea by looking for the presence of its toxin as well as by culturing. Enzyme immunoassay (EIA, Premier toxins A and B; Meridian Diagnostic Inc.) was used to detect toxin from 237 fresh stool samples collected from HIV-positive patients with diarrhoea. Culture was done on cycloserine-cefoxitin-fructose agar and brain- heart infusion agar.

RESULTS

C. difficile was found in 12 of 237 (5.1%, 95% CI 2.64%-8.68%) HIV-positive patients with diarrhoea (9 patients were positive by EIA and 3 by culture). The presence of C. difficile in patients who had received antiretroviral therapy (7/66 [10.6%]) was significantly higher (p < 0.016) compared with those who had not (5/171 [3%]). Of the 12 patients positive for C. difficile, 7 were on antiretroviral therapy for a mean (SD) of 34.4 months with mean CD4+ count of 186 (98.81) cells/cmm and 5 patients were anti-retroviral-naïve with mean CD4+ count of 181 (68.7) cells/cmm. All the 12 patients were on antibiotics for previous 2 months and 4 of 12 had been hospitalized in the previous 30 days.

CONCLUSION

C. difficile infections occurred more frequently in patients who had received antiretroviral therapy. Our study population had a lower frequency of C. difficile infections compared to previous studies.

Mode-locked thulium bismuth codoped fiber laser using graphene saturable absorber in ring cavity: reply

Jung and Lee have made comments [Appl. Opt.53, 553-554 (2014)] on "Mode-locked thulium bismuth codoped fiber laser using Graphene saturable absorber in ring cavity" [Appl. Opt.52, 1226-1229 (2013)]. The answer for the comment is provided in this report.

The Outcomes of Short Term Inspiratory Muscle Training (IMT) Combined with Chest Physiotherapy in Hospitalized COPD Patients

Objective: The objective of this study was to identify the outcomes of short term inspiratory muscle training (IMT) combined with chest physiotherapy (CP) on lung function, inspiratory muscle strength, exercise tolerance and quality of life of COPD patients. Materials and Methods: This randomized-controlled trial was conducted at the Terendak Armed Forces Hospital, Melaka. Eighteen hospitalized COPD patients (FEV1 50% to = 80% predicted) were randomized into intervention (IG) and control group (CG). The IG received IMT and CP treatments whilst the CG received only CP for a period of 4 weeks. Assessments of lung function (FEV1/FVC), inspiratory muscle strength (PImax), exercise tolerance (6MWT) and quality of life (SGRQ score) were taken at baseline and after 4 weeks. Results: Analysis showed IG group increased in FEV1/FVC by 19.4%, PImax by 54.7%, 6MWT by 33.2% and quality of life by 52.6% (All, p<0.05). The control group increased in FEV1/FVC by 8.7% (p>0.05), PImax by 15% (p<0.05), 6MWT by 18.9% (p<0.05) and quality of life by 15.6% (p<0.05). Conclusion: The present study has established that by combining inspiratory muscle training (IMT) and chest physiotherapy, provides superior effects on lung function, inspiratory muscle strength, exercise tolerance and quality of life among COPD patients. DOI: http://dx.doi.org/10.3329/bjms.v12i4.13302 Bangladesh Journal of Medical Science Vol. 12 No. 04 October ’13 Page 398-404

Rapid identification of clinical mycobacterial isolates by protein profiling using matrix assisted laser desorption ionization-time of flight mass spectrometry

PURPOSE

The purpose of this study was to evaluate the identification of Mycobacterium tuberculosis which is often plagued with ambiguity. It is a time consuming process requiring 4-8 weeks after culture positivity, thereby delaying therapeutic intervention. For a successful treatment and disease management, timely diagnosis is imperative. We evaluated a rapid, proteomic based technique for identification of clinical mycobacterial isolates by protein profiling using matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS).

MATERIALS AND METHODS

Freshly grown mycobacterial isolates were used. Acetonitrile/trifluoroacetic acid extraction procedure was carried out, following which cinnamic acid charged plates were subjected to identification by MALDI-TOF MS.

RESULTS

A comparative analysis of 42 clinical mycobacterial isolates using the MALDI-TOF MS and conventional techniques was carried out. Among these, 97.61% were found to corroborate with the standard methods at genus level and 85.36% were accurate till the species level. One out of 42 was not in accord with the conventional assays because MALDI-TOF MS established it as Mycobacterium tuberculosis (log (score)>2.0) and conventional methods established it to be non-tuberculous Mycobacterium.

CONCLUSIONS

MALDI-TOF MS was found to be an accurate, rapid, cost effective and robust system for identification of mycobacterial species. This innovative approach holds promise for early therapeutic intervention leading to better patient care.

Direct period measurement for fiber Bragg grating using an optical imaging technique

This paper proposes an approach based on an optical imaging technique for the period measurement of fiber Bragg gratings (FBG). The simple, direct technique involves a differential interface contrast (DIC) microscope and a high-resolution CCD camera. Image processing is performed on the microscope images to obtain low-noise grating profiles and then the grating periods. Adopting a large image sample size in the image processing can reduce uncertainty. During the investigation, FBGs of different grating periods are fabricated by prestraining the photosensitive fibers during the UV-writing process. A good linearity between the measured Bragg wavelengths and grating periods is observed and the measured strain-optics coefficient was found to be in agreement with reported literature.

Mode-locked thulium-bismuth codoped fiber laser using graphene saturable absorber in ring cavity

We demonstrate mode locking of a thulium-bismuth codoped fiber laser (TBFL) operating at 1901.6 nm, using a graphene-based saturable absorber (SA). In this work, a single layer graphene is mechanically exfoliated using the scotch tape method and directly transferred onto the surface of a fiber pigtail to fabricate the SA. The obtained Raman spectrum characteristic indicates that the graphene on the core surface has a single layer. At 1552 nm pump power of 869 mW, the mode-locked TBFL self starts to generate an optical pulse train with a repetition rate of 16.7 MHz and pulse width of 0.37 ps. This is a simple, low-cost, stable, and convenient laser oscillator for applications where eye-safe and low-photon-energy light sources are required, such as sensing and biomedical diagnostics.

Micro-bending based optical band-pass filter and its application in S-band Thulium-doped fiber amplifier

A new approach for filtering an optical band-pass in optical amplifier is proposed using a macro bending. The proposed filter leverages the bending loss of higher order modes at shorter wavelengths. At longer wavelengths, the filter increases fiber's bending loss as the fundamental mode 'tail' is leak out from the cladding. The combination of wavelength dependent loss at longer and shorter wavelength gives rise to the optical band-pass filter characteristic inside the fiber. The simulated spectral response of the filter is found to be in good agreement with the experimental results. Subsequently, the proposed optical band-pass filter is applied in Thulium-doped fiber amplifiers (TDFA) system for gain and noise figure enhancements. The filter functions to suppress both the amplified spontaneous emission (ASE) at 800 nm and 1800 nm wavelength regions and thus improves both gain and noise figure performances in S-band region. By bending of the gain medium, gain and noise figure of the TDFA are improved by about 2 dB and 0.5 dB respectively, within a wavelength region from 1440 and 1500 nm when the 1050 nm pump power is fixed at 250 mW.