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.

S-band multiwavelength ring Brillouin/Raman fiber laser with 20 GHz channel spacing

We propose and demonstrate a tunable S-band multiwavelength Brillouin/Raman fiber laser (MBRFL) with a tuning range of between 1490 to 1530 nm. The proposed MBRFL is designed around a 7.7 km long dispersion compensating fiber in a simple ring configuration, acting as a nonlinear medium for the generation of multiple wavelengths from stimulated Brillouin scattering (SBS) and also as a nonlinear gain medium for stimulated Raman scattering (SRS) amplification. A laser source with a maximum power of 12 dBm acts as the Brillouin pump (BP), while two 1420 nm laser diodes with a total power of 26 dBm act as the Raman pumps (RPs). The MBRFL can generate a multiwavelength comb consisting of even and odd Stokes at an average power of -12 dBm and -14 dBm respectively, and by separating the even and odd Stokes outputs, a 20 GHz channel spacing is obtained between two consecutive wavelengths. Due to the four-wave mixing (FWM) effect, anti-Stokes lines are also observed. The multiwavelength comb generated is not dependent on the BP, thus providing high stability and repeatability and making it a highly potential source for many real-world applications. This is the first time, to the knowledge of the authors, that a tunable MBRFL has been developed using SRS to obtain gain in the S-band region.

Spreading profile of evaporative liquid drops in thin porous layer

Spreading of evaporative liquid drops in a thin porous layer has been studied. The entire spreading process can be divided into three distinct phases according to the change of the wetted porous region size. The first phase is characterized by the expansion of the wetted porous region and shrinking of the liquid drop. Contact line pinning is observed in the wetted porous region in the second phase even with the liquid drop totally absorbed into the porous layer. The third phase sees the shrinkage of the wetted porous region until it is not observable. Based on these observations, a model is devised to simulate the spreading of a liquid drop under the studied conditions. Partial differential equations are used to describe the relation between liquid drop volume and other important parameters of a fluid flow, including maximum wetted region diameter achieved, time taken to reach each spreading process phase, and evaporation rate. Calculated results are in good agreement with the experimental data.

Note: Fabrication of tapered fibre tip using mechanical polishing method

Tapered fibre tips fabricated using mechanical polishing method is studied. The fibre tips are formed by sequential polishing flat-ended single mode fibres with decreasing aluminium oxide polishing film grit size. Based on the proposed technique, tapered fibre tips with cone angle ranging from 30° to 130° are fabricated by controlling the polishing angle. Besides the variety of cone angle, considerable smoothness of the fibre tip surface may assist in good metal coating and hence a well-defined aperture can be obtained. In addition, this paper presents a two-step hybrid fabrication method combining the proposed polishing method with chemical etching method to increase the possible fibre tip cone angles achievable by chemical etching method.

Efficient and Compact Optical Amplifier Using EYDF

An efficient Erbium/Ytterbium doped fiber amplifier (EYDFA) is demonstrated using a 1058nm pumping wavelength, where the amplification is assisted by energy transfer between Yb and Er ions. The energy transfer increases the limit of erbium doping concentration that is imposed by concentration quenching in Erbium-doped fiber (EDF). Therefore, the gain and noise figure are severely degraded with 1480 nm pumping, where the energy transfer cannot be achieved. The use of optical isolator improves the small signal gain and noise figure by about 4.8 dB and 1.6 dB, respectively. By employing a double-pass configuration, a higher gain can be obtained with an expense of a noise figure penalty. The gain improvement of 17.0 dB is obtained at 20 mW and -50 dBm of pump and input signal powers. This shows that the double-pass configuration is an important aspect to consider when designing an efficient EYDFA.

Performance comparison of Zr-based and Bi-based erbium-doped fiber amplifiers

In this Letter, we present a comprehensive comparison of the performance of a zirconia-based erbium-doped fiber amplifier (Zr-EDFA) and a bismuth-based erbium-doped fiber amplifier (Bi-EDFA). The experimental results reveal that a Zr-EDFA can achieve comparable performance to the conventional Bi-EDFA for C-band and L-band operations. With a combination of both Zr and Al, we could achieve a high erbium-doping concentration of about 2800 ppm (parts per million) in the glass host without any phase separations of rare earths. The Zr-based erbium-doped fiber (Zr-EDF) was fabricated using in a ternary glass host, zirconia-yttria-aluminum codoped silica fiber through a solution-doping technique along with modified chemical vapor deposition. At a high input signal of 0 dBm, a flat gain at average value of 13 dB is obtained with a gain variation of less than 2 dB within the wavelength region of 1530-1575 nm and using 2 m of Zr-EDF and 120 mW pump power. The noise figures are less than 9.2 at this wavelength region. It was found that a Zr-EDFA can achieve even better flat-gain value and bandwidth as well as lower noise figure than the conventional Bi-EDFA.

Multi-wavelength laser generation with Bismuthbased Erbium-doped fiber

A multi-wavelength laser comb is demonstrated using a nonlinear effect in a backward pumped Bismuth-based Erbium-doped fiber (Bi-EDF) for the first time. It uses a ring cavity resonator scheme containing a 215 cm long highly nonlinear Bi-EDF, optical isolators, polarisation controller and 10 dB output coupler. The laser generates more than 10 lines of optical comb with a line spacing of approximately 0.41 nm at 1615.5 nm region using 146 mW of 1480 nm pump power.

Compact Brillouin-erbium fiber laser

A single-wavelength Brillouin fiber laser (BFL) is demonstrated at the extended L-band region using bismuth-based erbium-doped fiber (Bi-EDF) for the first time to the best of our knowledge. A 2.15-m-long Bi-EDF is used to provide both nonlinear and linear gains to generate a stimulated Brillouin scattering (SBS) and to amplify the generated SBS, respectively. The BFL operates at 1613.93 nm, which is upshifted by 0.09 nm from the Brillouin pump with a peak power of 2 dBm and a side-mode suppression ratio of more than 22 dB. The generated BFL has a narrow linewidth and many potential applications, such as in optical communication and sensors.

Effects of different Raman pumping schemes on stimulated Brillouin scattering in a linear cavity

The effects of backward, forward, and bidirectional Raman pumping schemes on stimulated Brillouin scattering (SBS) is investigated in this study. By using a linear cavity, we utilize residual Brillouin pump (BP) and Raman pump (RP) power after each transmission through a 25 km single-mode fiber (SMF) used as a gain medium. The SBS threshold power is reduced in the forward, backward, and bidirectional Raman pumping schemes by 2.5, 1.75, and 2.75 dB, respectively when the 1480 nm RP power is fixed at 150 mW and the BP wavelength is 1580 nm. Surprisingly, it is revealed that the SBS threshold reduction depends strongly and solely on Raman gain and it is independent of the Raman pumping schemes. In addition, the effect of Raman amplification on SBS is more effective at the SBS threshold, especially in the bidirectional and forward schemes.

Linear cavity Brillouin fiber laser with improved characteristics

A configuration for linear cavity Brillouin fiber laser (BFL) generation is demonstrated using a standard single-mode fiber, two optical circulators, a 3 dB coupler, and a 95/5 coupler to allow high efficiency. With a Brillouin pump (BP) power of 13 dBm, the laser peak power is 12.3 dB higher than a conventional linear cavity BFL at an upshifted wavelength of 0.086 nm from the BP wavelength. In addition, it is revealed that the BFL peak power can be higher than the transmitted BP peak power when the BP power exceeds the second Brillouin Stokes threshold power.

Molecular characterization of Ephedra species found in Pakistan

Ephedra, also known as "ma huang", is a dioecious, drought- and frost-resistant, perennial, evergreen shrub with compelling medicinal value. The genus is represented by 42 species around the world, 9 of which were provisionally reported from Pakistan. Species of the genus have a controversial taxonomy due to their overlapping morphological features. Conventional tools alone are not sufficient for characterizing the species. The objective of present study was to assess the genetic variability present in different biotypes of Ephedra growing in Pakistan using molecular markers. A total of six genotypes collected from diverse geographic zones of Pakistan were used. The DNA of all genotypes was amplified using nine randomly amplified polymorphic DNA (RAPD) primers to study genetic variability at the molecular level. The dissimilarity coefficient matrix based on the data of 9 RAPD primers was used to construct a dendrogram which was then used to group the genotypes in clusters. Based on the dendrogram and dissimilarity coefficient matrix, the RAPD markers used here revealed a moderate to high level of genetic polymorphism (6 to 49%) among the genotypes. It was found that the collection of genotype accessions from Swat Valley in northwestern Pakistan was most distantly related to the other five collections. More molecular markers including functional genes and ribosomal spacer regions are suggested to find a better estimate of the genetic diversity present in Ephedra growing in Pakistan. The information provided here is useful for identifying valuable Ephedra variants which will be used for medicinal purposes and earning foreign currency.

Multiwavelength Brillouin/Erbium-Ytterbium fiber laser

A multi-wavelength Brillouin/Erbium-Ytterbium doped fiber laser which operates in the 1535 nm region is proposed and demonstrated. The system employs both linear and nonlinear gain from a 4 meter Erbium-Ytterbium doped fiber and an 8 km single mode fiber respectively to generate an optical comb with a spacing of approximately 0.084 nm. A stable output laser comb of more than 22 lines was obtained with a Brillouin pump of 2 dBm and a 1058 nm pump of 175 mW. A maximum peak power of -4.2 dBm was obtained at a wavelength of 1535.16 nm at these pump power settings while the spectral linewidth of the laser is approximately 8 Hz.

An efficient gain-flattened C-band Erbium-doped fiber amplifier

An efficient gain-flattened C-band Erbium-doped fibre amplifier is demonstrated using a double-pass configuration with an IsoGainTM Erbium-doped fibre (EDF). The amplifier utilizes a double-propagation of signal provided by an optical circulator at the output end of the EDF to obtain an improved flat-gain characteristic. At input signal power of -10 dBm, a flat-gain of 25 dB was obtained from wavelength region from 1528 to 1568 nm. This amplifier has the potential to be used in the high channel count dense wavelength division multiplexing system because of its simplicity and low cost.

Factors affecting abundance and oviposition rates of a field population of the Old World screw-worm fly, Chrysomya bezziana (Diptera: Calliphoridae)

Sentinel cattle and a grid of swormlure-baited sticky traps were used to monitor a Malaysian population of the Old World screw-worm fly, Chrysomya bezziana Villeneuve. Observations were carried out on an isolated cattle station at monthly intervals during the period August 1996 to June 2000. The number of flies caught was unaffected by weather conditions at the time of trapping, but was positively correlated with the total rainfall and the average daily air temperature prevailing 15-28 days earlier, when trapped flies were still juveniles. Trap catches were biased in favour of females, but daily catch rates of both sexes increased significantly the longer traps were open, suggesting that efficacy was related to the differential volatility of the chemicals comprising swormlure. Oviposition on sentinel cattle occurred mostly in late afternoon or early evening but increased significantly as the wound aged. Oviposition rates were positively correlated with female catch rates, but the relationship was curvilinear, suggesting that fly populations may be subject to some form of density-dependent constraint. Consistent differences in oviposition rates on sentinel cattle at different localities on the cattle station suggested the existence of highly clumped, quasi-stationary populations. Differences in trap catches between traps located in pastoral areas and those sited in nearby oil palm or rubber plantations supported this interpretation of the data. These findings are discussed in relation to the use of the sterile insect technique for the control of screw-worm fly infestations.

Primary pleural lymphomas

Two patients are presented with primary low grade pleural B cell lymphomas with no history of a pyothorax.

Differential inhibition of human cancer cell proliferation by citrus limonoids

Limonoids have been shown to inhibit the growth of estrogen receptor-negative and -positive human breast cancer cells in culture. The primary objective of this study was to test the antiproliferative activity of limonoids (obacunone 17 beta-D-glucopyranoside, nomilinic acid 17 beta-D-glucopyranoside, limonin, nomilin, and a limonoid glucoside mixture), found in high concentrations in mandarin (Citrus reticulata Blanco), against a series of human cancer cell lines. The human cancer cell lines included leukemia (HL-60), ovary (SKOV-3), cervix (HeLa), stomach (NCI-SNU-1), liver (Hep G2), and breast (MCF-7). The growth-inhibitory effects of the four limonoids and the limonoid glucoside mixture against MCF-7 cells were significant, and the antiproliferative activity of the different citrus limonoids was also dose and time dependent. No significant effects were observed on growth of the other cancer cell lines treated with the four individual limonoids at 100 micrograms/ml. At 100 micrograms/ml, the limonoid glucoside mixture demonstrated a partial inhibitory effect on SKOV-3 cancer cells. With use of flow cytometry, it was found that all the limonoid samples could induce apoptosis in MCF-7 cells at relatively high concentrations (100 micrograms/ml). Considering the high concentration needed to induce apoptosis, it is unlikely that this is the primary mechanism of action for the cytotoxic effects seen with limonoids in this study. Further work is needed in this area to establish the mechanism of action of citrus limonoids on human breast cancer cells.

Intrinsic aging vs. photoaging: a comparative histopathological, immunohistochemical, and ultrastructural study of skin

Cutaneous aging is a complex biological phenomenon affecting the different constituents of the skin. To compare the effects of intrinsic and extrinsic aging processes, a total of 83 biopsies were collected from sun-exposed and protected skin of healthy volunteers representing decades from the 1st to the 9th (6-84 years of age). Routine histopathology coupled with computer-assisted image analysis was used to assess epidermal changes. Immunoperoxidase techniques with antibodies against type I and type III collagens and elastin were used to quantitatively evaluate changes in collagen and elastic fibers and their ultrastructure was examined by transmission electron microscopy. Epidermal thickness was found to be constant in different decades in both sun-exposed and protected skin; however, it was significantly greater in sun-exposed skin (P = 0.0001). In protected skin, type I and III collagen staining was altered only after the 8th decade, while in sun-exposed skin the relative staining intensity significantly decreased from 82.5% and 80.4% in the 1st decade to 53.2% and 44.1% in the 9th decade, respectively (P = 0.0004 and 0.0008). In facial skin the collagen fiber architecture appeared disorganized after the 4th decade. The staining intensity of elastin in protected skin significantly decreased from 49.2% in the 1st decade to 30.4% in the 9th decade (P = 0.05), whereas in sun-exposed skin the intensity gradually increased from 56.5% in the 1st decade to 75.2% in the 9th decade (P = 0.001). The accumulated elastin in facial skin was morphologically abnormal and appeared to occupy the areas of lost collagen. Collectively, the aging processes, whether intrinsic or extrinsic, have both quantitative and qualitative effects on collagen and elastic fibers in the skin.