Using Giant Pulses to Measure the Impulse Response of the Interstellar Medium

Giant pulses emitted by PSR B1937+21 are bright, intrinsically impulsive bursts. Thus, the observed signal from a giant pulse is a noisy but direct measurement of the impulse response from the ionized interstellar medium. We use this fact to detect 13,025 giant pulses directly in the baseband data of two observations of PSR B1937+21. Using the giant pulse signals, we model the time-varying impulse response with a sparse approximation method, in which the time dependence at each delay is decomposed in Fourier components, thus constructing a wavefield as a function of delay and differential Doppler shift. We find that the resulting wavefield has the expected parabolic shape, with several diffuse structures within it, suggesting the presence of multiple scattering locations along the line of sight. We also detect an echo at a delay of about 2.4 ms, over 1.5 times the rotation period of the pulsar, which between the two observations moves along the trajectory expected from geometry. The structures in the wavefield are insufficiently sparse to produce a complete model of the system, and hence the model is not predictive across gaps larger than about the scintillation time. Nevertheless, within its range, it reproduces about 75% of the power of the impulse response, a fraction limited mostly by the signal-to-noise ratio of the observations. Furthermore, we show that by deconvolution, using the model impulse response, we can successfully recover the intrinsic pulsar emission from the observed signal.Comment: 14 pages, 8 figures, Accepted for publication in Ap

Intrinsic Emission of PSR B1937+21 at 327 MHz

At 327 MHz, the observed emission of PSR B1937+21 is greatly affected by scattering in the interstellar medium, on a timescale of order the pulse period. We use the bright impulsive giant pulses emitted by the pulsar to measure the impulse response of the interstellar medium and then recover the intrinsic emission of the pulsar by deconvolution -- revealing fine structure on timescales not normally observable. We find that the intrinsic widths of the main pulse and interpulse in the pulse profile are similar to those measured at higher frequencies. We detect 60,270 giant pulses which typically appear as narrow, ~100 ns bursts consisting of one to few nanoshots with widths $\lesssim \! 10$ ns. However, about 10% of the giant pulses exhibit multiple bursts which seem to be causally related to each other. We also report the first detection of giant micropulses in PSR B1937+21, primarily associated with the regular main pulse emission. These are distinct from giant pulses not only in the phases at which they occur, but also in their larger widths, of order a microsecond, and steeper energy distribution. These measurements place useful observational constraints on emission mechanisms for giant pulses as well as the regular radio emission of millisecond pulsars.Comment: 55 pages, 48 figures, submitted to Ap

What is Core to A Brand? An Examination of The Brand Elements and Their Subsequent Impact on the Consumer

Abstract: The number of brands is proliferating. Approximately 3000 brands are introduced each year into supermarkets. There were at the time of writing 750 nameplates of cars, over 150 brands of lipstick, and 93 cat-food brands(Aaker, 1991, p. 8). Fifteen years down the line, undoubtedly this number has increased substantially. The propagation of media and distribution channels, have provided a thrust to the view that the brand and what it represents is the most important asset for many companies and is the basis for competitive advantage and profits (Keller, 2003). In support, Davis (2000) and Sheppard (1994) share a common view that brands are among a company's most powerful assets. From these opinions, it is clear to see the importance and benefits of owning a strong and memorable brand and this seems to be the core agenda of all major companies. It is believed by the researcher that academics, managers and other professionals would all benefit from understanding what elements are at the heart of a successful brand and as such, this document aims to provide a thorough understanding of the diverse elements of branding and investigate the importance of each element in the consumers mind. The researcher tries to accomplish his set objectives by using the primary research method of focus groups. The results from this research indicate that there are three core elements out of the various elements put under the scanner, which provided a basis for recommendations for further research

Gate controlled large resistance switching driven by charge density wave in 1T-TaS2/2H-MoS2 heterojunction

1T-TaS2 is a layered material that exhibits charge density wave (CDW) induced distinct electrical resistivity phases and has attracted a lot of attention for interesting device applications. However, such resistivity switching effects are often weak, and cannot be modulated by an external gate voltage - limiting their widespread usage. Using a back-gated 1T-TaS2/2H-MoS2 heterojunction, here we show that the usual resistivity switching in TaS2 due to different phase transitions is accompanied with a surprisingly strong modulation in the Schottky barrier height (SBH) at the TaS2/MoS2 interface - providing an additional knob to control the degree of the phase-transition-driven resistivity switching by an external gate voltage. In particular, the commensurate (C) to triclinic (T) phase transition results in an increase in the SBH owing to a collapse of the Mott gap in TaS2. The change in SBH allows us to estimate an electrical Mott gap opening of ~71 +/- 7 meV in the C phase of TaS2. On the other hand, the nearly-commensurate (NC) to incommensurate (IC) phase transition results in a suppression in the SBH, and the heterojunction shows a gate-controlled resistivity switching up to 17.3, which is ~14.5 times higher than that of standalone TaS2. The findings mark an important step forward showing a promising pathway to externally control as well as amplify the CDW induced resistivity switching. This will boost device applications that exploit these phase transitions, such as ultra-broadband photodetection, negative differential conductance, fast oscillator and threshold switching in neuromorphic circuits.Comment: Accepted for publication in Physical Review Applie

Functional outcome of locking anatomical plate in extra articular fractures of the distal humerus

Background: Extra articular distal humerus fractures are difficult to treat with conventional implants like intra medullary nail, 4.5 DCP and dual plate. The present study aims to study the functional outcome of the extra articular distal humerus plate (EADHP).Methods: 48 patients with displaced extra articular distal humerus fractures were included in the study. Inclusion criteria were age more than 18 years, closed fractures with or without radial nerve palsy and less than 3 weeks old trauma. Patients aged less than 18 years, those having open fractures, fractures more than 3 weeks old, non – unions and pathological fractures were excluded from the study. All patients were operated with EADHP. Clinically, the outcome was assessed by the disability of arm, shoulder and hand (DASH) score and elbow range of motion radiologically, union was evaluated on anteroposterior and lateral radiographs.Results: Out of 48 patients, 12 had AO type 12 A1 fracture, 26 patients had type B1 fractures and remaining 10 had type C1 fractures. Mean DASH score at final follow up was 18.1; range being 12.6 to 35.7 points. The mean elbow range of motion was 0 to 130 degrees (range: 120 to 140 degrees). The mean duration for complete radiological fracture union was 14 weeks, range being 12 to 18 weeks.Conclusions: The extraarticular distal humerus plate is an ideal implant for the fixation of distal humerus fractures since it provides good stability of fracture and enables early return to function