5,972 research outputs found
Spatial-temporal evolution of the current filamentation instability
The spatial-temporal evolution of the purely transverse current filamentation
instability is analyzed by deriving a single partial differential equation for
the instability and obtaining the analytical solutions for the spatially and
temporally growing current filament mode. When the beam front always encounters
fresh plasma, our analysis shows that the instability grows spatially from the
beam front to the back up to a certain critical beam length; then the
instability acquires a purely temporal growth. This critical beam length
increases linearly with time and in the non-relativistic regime it is
proportional to the beam velocity. In the relativistic regime the critical
length is inversely proportional to the cube of the beam Lorentz factor
. Thus, in the ultra-relativistic regime the instability
immediately acquires a purely temporal growth all over the beam. The analytical
results are in good agreement with multidimensional particle-in-cell
simulations performed with OSIRIS. Relevance of current study to recent and
future experiments on fireball beams is also addressed
Magnetically assisted self-injection and radiation generation for plasma based acceleration
It is shown through analytical modeling and numerical simulations that
external magnetic fields can relax the self-trapping thresholds in plasma based
accelerators. In addition, the transverse location where self-trapping occurs
can be selected by adequate choice of the spatial profile of the external
magnetic field. We also find that magnetic-field assisted self-injection can
lead to the emission of betatron radiation at well defined frequencies. This
controlled injection technique could be explored using state-of-the-art
magnetic fields in current/next generation plasma/laser wakefield accelerator
experiments.Comment: 7 pages, 4 figures, accepted for publication in Plasma Physics and
Controlled Fusio
Indications of superconductivity in doped highly oriented pyrolytic graphite
We have observed possible superconductivity using standard resistance vs.
temperature techniques in phosphorous ion implanted Highly Oriented Pyrolytic
Graphite. The onset appears to be above 100 K and quenching by an applied
magnetic field has been observed. The four initial boron implanted samples
showed no signs of becoming superconductive whereas all four initial and eight
subsequent samples that were implanted with phosphorous showed at least some
sign of the existence of small amounts of the possibly superconducting phases.
The observed onset temperature is dependent on both the number of electron
donors present and the amount of damage done to the graphene sub-layers in the
Highly Oriented Pyrolytic Graphite samples. As a result the data appears to
suggest that the potential for far higher onset temperatures in un-damaged
doped graphite exists.Comment: 7 pages, 1 table, 5 figures, 11 references, Acknowledgments section
was correcte
Magnetic control of particle-injection in plasma based accelerators
The use of an external transverse magnetic field to trigger and to control
electron self-injection in laser- and particle-beam driven wakefield
accelerators is examined analytically and through full-scale particle-in-cell
simulations. A magnetic field can relax the injection threshold and can be used
to control main output beam features such as charge, energy, and transverse
dynamics in the ion channel associated with the plasma blowout. It is shown
that this mechanism could be studied using state-of-the-art magnetic fields in
next generation plasma accelerator experiments.Comment: 10 pages, 3 figure
Higher order antibunching is not a rare phenomenon
Since the introduction of higher order nonclassical effects, higher order
squeezing has been reported in a number of different physical systems but
higher order antibunching is predicted only in three particular cases. In the
present work, we have shown that the higher order antibunching is not a rare
phenomenon rather it can be seen in many simple optical processes. To establish
our claim, we have shown it in six wave mixing process, four wave mixing
process and in second harmonic generation process.Comment: 6 pages, no figure, Latex 2
Sensitivity Enhancement of a Concave Shaped Optical Fiber Refractive Index Sensor Covered with Multiple Au Nanowires
In the present paper, a new kind of concave shaped refractive index sensor (CSRIS) exploiting localized surface plasmon resonance (LSPR) is proposed and numerically optimized. The LSPR effect between polaritons and the core guided mode of designed CSRIS is used to enhance the sensing performance. The sensor is characterized for two types of sensing structures coated with gold (Au) film and Au nanowires (AuNWs), respectively. The influence of structural parameters such as the distance (D) of the concave shaped channel (CSC) from the core, the diameter of the nanowire (dn) and the size (s) of the CSC are investigated here. In comparison to Au film, the AuNWs are shown to significantly enhance the sensitivity and the performance of the designed sensor. An enhanced sensitivity of 4471 nm/RIU (refractive index unit) is obtained with AuNWs, for a wide range of analytes refractive index (na) varying between 1.33 to 1.38. However, for conventional Au film; the sensitivity of 808.57 nm/RIU is obtained for the same range of analytes
A comparative study of dexmedetomidine versus clonidine in epidural anaesthesia to assess the level of sedation in patients undergoing lower abdominal and lower limb surgery
Background: To compare study of dexmedetomidine versus clonidine in epidural anesthesia to assess the level of sedation in patients undergoing lower abdominal and lower limb surgery.Methods: This was a comparative study conducted on admitted ASA grade I and II patients undergoing lower abdominal and lower limb surgeries. The patients were divided into three groups of 30 patients each, according to the epidural medication they received:-Group A-received 15ml of bupivacaine (0.5%) and dexmedetomidine (1.0µg/kg body weight) in 1ml of normal saline; Group B-received 15ml of bupivacaine (0.5%) and clonidine (2.0µg/kg body weight) in 1ml of normal saline; Group C-received 15ml of bupivacaine (0.5%) with 1ml of normal saline. The heart rate, blood pressure, sensory dermatome level, Motor blocked level, pain and VAS were recorded at different time intervals. The side effects were also noted.Results: The baseline parameters were comparable among the groups. All the hemodynamic parameters and other study parameters were similar at Min. 0. All the hemodynamic parameters such as heart rate, blood pressure and SpO2 were variable at different time intervals. Motor block level  was significantly (p<0.05) lower in Group C than Group A and Group B from Min 50 to Min 90. The sedation score was observed to be nil in Group C. The post-op pain score became higher in Group C than Group A and Group B at subsequent time intervals. A 3 (10%) of the rescue agents was observed in Group C. Atropine (30%) and mephenteramine (10%) were common rescue agents in Group B. The bradycardia was observed in 30% patients of Group B and in 40% of Group A.Conclusions: On addition of dexmedetomidine as adjuvant to bupivacaine in epidural anesthesia provides better anesthesia and sedation than clonidine as adjuvant to bupivacaine or bupivacaine alone with mild hemodynamic changes which are easily manageable
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Metal Nanowire Assisted Hollow Core Fiber Sensor for an Efficient Detection of Small Refractive Index Change of Measurand Liquid
In this article, a cost-effective hollow core fiber (HCF)-based refractive index (RI) sensor using surface plasmon resonance (SPR) is designed and demonstrated. The sensor consists of a metal nanowire inside an HCF along with the sensing medium of various refractive indices. SPR effect between polaritons and the guided core mode of designed HCF is exploited to enhance the sensing performance. A full vectorial finite element method (FEM) is used for the design and analyses of the sensing probes which exhibit very high sensitivities of 12,400 nm/RIU, 10560 nm/RIU, and 6400 nm/RIU for copper (Cu), gold (Au), and silver (Ag), respectively with a resolution of 1.61 × 10−6 RIU. Additionally, the influence of metal wire dimension is also investigated in this paper. The reported simple and low-cost sensor exhibits high sensitivity for liquid with refractive indices slightly higher than that of the dielectric tube, such as olive oil, turpentine, kerosene, chloroform, carbon tetrachloride, glycerol, and toluene
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