Risk of cardiac pacemaker pocket infection in a tertiary care hospital.

BACKGROUND: The risk of pacemaker pocket infections (PPIs) is rare with good antisepsis techniques and use of advanced antibiotics. However, injudicious antibiotic usage leads to the rise of multidrug-resistant bacteria, which may cause PPI. Few reports exist about the microbial spectrum of the PPI from our country, prompting us to study the same. METHODS: We conducted this retrospective observational study for 3 years (January 2013-February 2016) from all the patients with PPI. We collected the relevant clinical samples (blood and pus) for the microbial culture using a standard protocol. We included 100 samples collected from the medical staff and the hospital environment as a control sample. The data were analyzed using appropriate statistical methods and a P< 0.05 was considered statistically significant. RESULTS: Our data showed that 17 out of 160 (10.6%) patients had PPI. Coagulase negative Staphylococcus sp. was isolated in 7 (41.2%) patients, followed by Staphylococcus aureus in 4 patients (23.5%). Other isolated bacteria include multidrug-resistant Burkholderia cepacia (n = 3), Mycobacterium abscessus (n = 2) and polymicrobial infection in a single patient. One out of hundred surveillance samples grew B. cepacia. CONCLUSION: Our data revealed a high incidence of Gram-positive cocci causing PPI. Every hospital should formulate their antibiotic policy based on the pattern of the hospital flora and their drug sensitivity.

Prevalence of Multidrug-resistant, Extensively Drug-resistant, and Pandrug-resistant Pseudomonas aeruginosa from a Tertiary Level Intensive Care Unit.

BACKGROUND: Infection by Pseudomonas aeruginosa is common in the Intensive Care Unit (ICU), leading to increased morbidity and mortality. The organism is classified into various phenotypes based on the drug resistance pattern, namely, drug-resistant (DR), multi-DR (MDR), extensively DR (XDR), and pan-DR (PDR). We aim to study the incidence of P. aeruginosa phenotypes in a tertiary level ICU. MATERIALS AND METHODS: We conducted this prospective, observational study for 2 years (January 2014-December 2015) and collected appropriate clinical samples (blood, urine, wound discharge, etc.,) from all the patients admitted to ICU. We excluded patients with known septicemia and P. aeruginosa infection. Group 1 comprised a total 1915 patient samples and Group 2 comprised 100 active surveillance samples, collected from the medical staff and the hospital environment. The data were analyzed using appropriate statistical methods, and a P < 0.05 was considered statistically significant. RESULTS: We isolated 597 pathogenic bacteria out of 1915 specimens, giving a culture positivity rate of 31.2%. Klebsiella (43%), Acinetobacter (22%), and P. aeruginosa (15%) were the top three isolated bacteria. None of the surveillance samples grew P. aeruginosa. Antibiotic resistance studies revealed that 47.7% of P. aeruginosa isolates were DR, 50% were MDR, and 2.3% were XDR phenotype. None of the strains showed PDR phenotype. CONCLUSION: Our data revealed a high prevalence of DR phenotypes of P. aeruginosa in the ICU. Judicious use of antibiotics and strict infection control measures are essential to reduce the prevalence of drug resistance.

Mid-infrared photodetectors operating over an extended wavelength range up to 90 K.

We report a wavelength threshold extension, from the designed value of 3.1 to 8.9 µm, in a p-type heterostructure photodetector. This is associated with the use of a graded barrier and barrier offset, and arises from hole-hole interactions in the detector absorber. Experiments show that using long-pass filters to tune the energies of incident photons gives rise to changes in the intensity of the response. This demonstrates an alternative approach to achieving tuning of the photodetector response without the need to adjust the characteristic energy that is determined by the band structure.

Non-universality of scaling exponents in quantum Hall transitions.

We have investigated experimentally the scaling behaviour of quantum Hall transitions in GaAs/AlGaAs heterostructures of a range of mobility, carrier concentration, and spacer layer width. All three critical scaling exponents γ, κ and p were determined independently for each sample. We measure the localization length exponent to be γ ≈ 2.3, in good agreement with expected predictions from scaling theory, but κ and p are found to possess non-universal values. Results obtained for κ range from κ = 0.16 ± 0.02 to κ = 0.67 ± 0.02, and are found to be Landau level (LL) dependent, whereas p is found to decrease with increasing sample mobility. Our results demonstrate the existence of two transport regimes in the LL conductivity peak; universality is found within the quantum coherent transport regime present in the tails of the conductivity peak, but is absent within the classical transport regime found close to the critical point at the centre of the conductivity peak. We explain these results using a percolation model and show that the critical scaling exponent depends on certain important length scales that correspond to the microscopic description of electron transport in the bulk of a two-dimensional electron system.

Terahertz inverse synthetic aperture radar imaging using self-mixing interferometry with a quantum cascade laser.

We propose a terahertz (THz)-frequency synthetic aperture radar imaging technique based on self-mixing (SM) interferometry, using a quantum cascade laser. A signal processing method is employed which extracts and exploits the radar-related information contained in the SM signals, enabling the creation of THz images with improved spatial resolution. We demonstrate this by imaging a standard resolution test target, achieving resolution beyond the diffraction limit.

Measurement of the intrinsic linewidth of terahertz quantum cascade lasers using a near-infrared frequency comb.

We report the measurement of the frequency noise power spectral density of a quantum cascade laser emitting at 2.5THz. The technique is based on heterodyning the laser emission frequency with a harmonic of the repetition rate of a near-infrared laser comb. This generates a beatnote in the radio frequency range that is demodulated using a tracking oscillator allowing measurement of the frequency noise. We find that the latter is strongly affected by the level of optical feedback, and obtain an intrinsic linewidth of ~230Hz, for an output power of 2mW.

Mode-locking of a terahertz laser by direct phase synchronization.

A novel scheme to achieve mode-locking of a multimode laser is demonstrated. Traditional methods to produce ultrashort laser pulses are based on modulating the cavity gain or losses at the cavity roundtrip frequency, favoring the pulsed emission. Here, we rather directly act on the phases of the modes, resulting in constructive interference for the appropriated phase relationship. This was performed on a terahertz quantum cascade laser by multimode injection seeding with an external terahertz pulse, resulting in phase mode-locked terahertz laser pulses of 9 ps duration, characterized unambiguously in the time domain.

Integrated injection seeded terahertz source and amplifier for time-domain spectroscopy.

We used a terahertz (THz) quantum cascade laser (QCL) as an integrated injection seeded source and amplifier for THz time-domain spectroscopy. A THz input pulse is generated inside a QCL by illuminating the laser facet with a near-IR pulse from a femtosecond laser and amplified using gain switching. The THz output from the QCL is found to saturate upon increasing the amplitude of the THz input power, which indicates that the QCL is operating in an injection seeded regime.

Phase-locking of a 2.5 THz quantum cascade laser to a frequency comb using a GaAs photomixer.

We report the heterodyne detection and phase locking of a 2.5 THz quantum cascade laser (QCL) using a terahertz frequency comb generated in a GaAs photomixer using a femtosecond fiber laser. With 10 mW emitted by the QCL, the phase-locked signal at the intermediate frequency yields 80 dB of signal-to-noise ratio in a bandwidth of 1 Hz.

Measurement and analysis of the diffuse reflectance of powdered samples at terahertz frequencies using a quantum cascade laser.

We report terahertz (THz) diffuse reflectance measurements of bulk powdered samples at a frequency of 2.83 THz using a narrowband quantum cascade laser. Samples studied comprise polydisperse powders with absorption coefficients extending over two orders of magnitude from ∼3 cm(-1) to >200 cm(-1). Diffuse reflectance measurements are used to obtain the effective absorption coefficient of these samples from the backscattering cross-section, predicted under the quasi-crystalline approximation (QCA) in the T-matrix formulation and in conjunction with the Percus-Yevick pair distribution function. Results are compared with effective absorption coefficients obtained from THz time-domain spectroscopy measurements on pressed pellet samples, and show good agreement over the range of effective absorption coefficients studied. We observe that the backscattering cross-section predicted under the QCA is strongly dependent on both the real and imaginary components of the complex permittivity of the sample, and we show that reliable determination of the absorption coefficient from diffuse reflectance measurements therefore requires knowledge of the sample's refractive index. This work demonstrates the applicability of diffuse reflectance measurements, using a THz frequency quantum cascade laser, to the high-resolution spectroscopic analysis of bulk powdered samples at THz frequencies.

Terahertz ambipolar dual-wavelength quantum cascade laser.

Terahertz frequency quantum cascade lasers (THz QCLs) are compact solid-state sources of terahertz radiation that were first demonstrated in 2002. They have a broad range of potential applications ranging from gas sensing and non-destructive testing, through to security and medical imaging, with many polycrystalline compounds having distinct fingerprint spectra in the terahertz frequency range. In this article, we demonstrate an electrically-switchable dual-wavelength THz QCL which will enable spectroscopic information to be obtained within a THz QCL-based imaging system. The device uses the same active region for both emission wavelengths: in forward bias, the laser emits at 2.3 THz; in reverse bias, it emits at 4 THz. The corresponding threshold current densities are 490 A/cm(2) and 330 A/cm(2), respectively, with maximum operating temperatures of 98K and 120 K.

Predictable surface emission patterns in terahertz photonic-crystal quantum cascade lasers.

We demonstrate a framework to understand and predict the far-field emission in terahertz frequency photonic-crystal quantum cascade lasers. The devices, which employ a high-performance three-well active region, are lithographically tunable and emit in the 104-120 microm wavelength range. A peak output power of 7 mW in pulsed mode is obtained at 10 K, and the typical device maximum operating temperature is 136 K. We identify the photonic-crystal band-edge states involved in the lasing process as originating from the hexapole and monopole modes at the G point of the photonic band structure, as designed. The theoretical far-field patterns, obtained via finite-difference time-domain simulations, are in excellent agreement with experiment. Polarization measurements further support the theory, and the role of the bonding wires in the emission process is elucidated.

Generation of Bessel beams using a terahertz quantum cascade laser.

We report the generation of Bessel beams using polytetrafluoroethene conical lenses and a quantum cascade laser emitting at 2.8 THz. The formation of a central beam spot that retains its size over distances exceeding the characteristic Rayleigh range is demonstrated, and the power transport properties of these beams are compared with those obtained using parabolic reflectors. These lenses could provide an attractive alternative to parabolic reflectors for terahertz imaging applications where a large depth of focus and/or efficient and controllable coupling of radiation onto a small target are desirable.

Electrically pumped photonic-crystal terahertz lasers controlled by boundary conditions.

Semiconductor lasers based on two-dimensional photonic crystals generally rely on an optically pumped central area, surrounded by un-pumped, and therefore absorbing, regions. This ideal configuration is lost when photonic-crystal lasers are electrically pumped, which is practically more attractive as an external laser source is not required. In this case, in order to avoid lateral spreading of the electrical current, the device active area must be physically defined by appropriate semiconductor processing. This creates an abrupt change in the complex dielectric constant at the device boundaries, especially in the case of lasers operating in the far-infrared, where the large emission wavelengths impose device thicknesses of several micrometres. Here we show that such abrupt boundary conditions can dramatically influence the operation of electrically pumped photonic-crystal lasers. By demonstrating a general technique to implement reflecting or absorbing boundaries, we produce evidence that whispering-gallery-like modes or true photonic-crystal states can be alternatively excited. We illustrate the power of this technique by fabricating photonic-crystal terahertz (THz) semiconductor lasers, where the photonic crystal is implemented via the sole patterning of the device top metallization. Single-mode laser action is obtained in the 2.55-2.88 THz range, and the emission far field exhibits a small angular divergence, thus providing a solution for the quasi-total lack of directionality typical of THz semiconductor lasers based on metal-metal waveguides.

Isolation, purification and immunological characterization of novel low molecular weight protein antigen CFP 6 from culture filtrate of M. tuberculosis.

A novel immunogenic antigen, CFP 6 was purified from culture filtrate of M. tuberculosis by a preparatory 2-D electrophoresis method. The protein focused at pI of 4.0 during isoelectric focusing. Molecular weight of the purified protein by ES MS was found to be 11.61 kD. N-terminal amino acid sequence of CFP 6 could be aligned to the deduced amino acid sequence from ORF Rv3004 and was found to be a novel protein with 112 aa residues. Single N-terminal sequence showed that the purified protein was essentially free from contaminants and the amino acid analysis of the antigen was in good agreement with the DNA sequence deduced amino acid composition. Purified CFP 6 was studied for its ability to induce proliferative responses of peripheral blood lymphocytes from five categories of human subjects. These were: untreated, active pulmonary tuberculosis patients; patients after 2-3 months of chemotherapy; vaccinated professional contacts; vaccinated/nonvaccinated healthy controls. CFP 6 elicited high proliferative responses in healthy contacts and patients recovering from the disease. This protein also induced the release of a significantly high amount of IFN-gamma in cell culture supernatant of healthy contacts as compared to other categories of subjects. This protein was further evaluated and compared with PPD and total CS for its DTH inducing ability in guinea pigs immunised with BCG or M. tuberculosis H(37)Rv. CFP 6 elicited a powerful immune response in vitro and in vivo animal model, hence seems to be an immunologically important protein.

Effect of exercise on pulmonary function tests in normal first degree relations of asthmatic subjects.

The prevalence of exercise-induced asthma (EIA) after six minutes of standard exercise test on bicycle ergometer was studied in thirty healthy first degree relations of asthmatic subjects (group II) and was compared with that in thirty healthy controls (group I). Pulmonary function tests (PFT) measuring FVC, FEV1, FEF25-75% and PEFR were performed on each subject prior of exercise, immediately following exercise period and serially at 5 minute interval for 25 minutes thereafter. Bronchial lability was noted in 7% and 27% of the subjects in groups I and II respectively. Of all the parameters measured, FEF25-75% exhibited most striking changes when expressed as % of the baseline value.