https://www.uni-lj.si/mma/biomedicina%20Macek%20Influenza%20virus%20budding/2013090613550890/

Influenza virus assembly and budding.

Influenza Virus M2 Protein Mediates ESCRT-Independent Membrane Scission

The Interferon-Inducible Protein Viperin Inhibits Influenza Virus Release by Perturbing Lipid Rafts

https://escholarship.org/content/qt7548q7cp/qt7548q7cp.pdf?t=qaem19

Assembly and budding of influenza virus.

We derive a stochastic nonlinear continuum theory to describe the morphological evolution of amorphous surfaces eroded by ion bombardment. Starting from Sigmund's theory of sputter erosion, we calculate the coefficients appearing in the continuum equation in terms of the physical parameters characterizing the sputtering process. We analyze the morphological features predicted by the continuum theory, comparing them with the experimentally reported morphologies. We show that for short time scales, where the effect of nonlinear terms is negligible, the continuum theory predicts ripple formation. We demonstrate that in addition to relaxation by thermal surface diffusion, the sputtering process can also contribute to the smoothing mechanisms shaping the surface morphology. We explicitly calculate an effective surface diffusion constant characterizing this smoothing effect, and show that it is responsible for the low temperature ripple formation observed in various experiments. At long time scales the nonlinear terms dominate the evolution of the surface morphology. The nonlinear terms lead to the stabilization of the ripple wavelength and we show that, depending on the experimental parameters such as angle of incidence and ion energy, different morphologies can be observed: asymptotically, sputter eroded surfaces could undergo kinetic roughening, or can display novel ordered structures with rotated ripples. Finally, we discuss in detail the existing experimental support for the proposed theory, and uncover novel features of the surface morphology and evolution, that could be directly tested experimentally.

Morphology of Ion-Sputtered Surfaces

In this work, decay spectroscopy of neutron-rich 43 K has been performed at the Radioactive Ion Beam (RIB) facility at Variable Energy Cyclotron Centre (VECC), Kolkata by producing it with an 18-MeV alpha beam on 40 Ar gas target. The beam was delivered from the K130 Cyclotron and the gas jet recoil transport system was used to move the products to a low-background site. The β-feeding intensities were measured by both high resolution γ-ray spectroscopy and total absorption γ-ray spectroscopy methods in order to address mainly the anomalies (if any) in the feeding to ΔJ ≥ 1 levels reported earlier. The decay half-life of 43 K was also measured to be 22.4(1) hrs.

/pdf/decay-measurements-of-43k-b-43ca-by-hrs-and-tas-1vjm9qimkt.pdf

Decay measurements of 43K(β−)43Ca by HRS and TAS

Development of an analog phase shifter for particle accelerator control circuits

Photofission of actinides is studied in the region of nuclear excitation energies that covers the entire giant dipole resonance (GDR) region. The mass distributions of 238U photofission fragments have been explored theoretically for eight different endpoint bremsstrahlung energies from 11.5 to 67.7 MeV, which correspond to average photon energies of 9.09 to 15.90 MeV. Among these energies, 29.1 MeV corresponds to the average photon energy of 13.7 ± 0.3 MeV, which coincides with the GDR peak for 238U photofission. The integrated yield of 238U photofission, as well as charge distribution of photofission products, is calculated and its role in producing nuclei and their neutron-richness is investigated.

/pdf/energy-dependence-of-exotic-nuclei-production-cross-sections-1apkqnj6m5.pdf

Energy dependence of exotic nuclei production cross sections by photofission reaction in GDR range

Theoretical study of an alternate phase focusing (APF) structure, realized in a long chain of double gap quarter wave resonators, capable of accelerating heavy ions from 1.3 to 7  MeV/u has been carried out. Mathieu-Hill stability analysis for the focusing periods consisting of independent resonators with phase variation satisfying square-wave law has been used to evaluate parameters such as the electric field and phase for the resonators. Furthermore, a smooth approximation method taking into account the acceleration in the linac has been employed to find out the rf bucket parameters (energy and phase width acceptance) of the focusing periods. Corroborative particle tracking (longitudinal and transverse) has been carried out using simulated 3D fields for double gap quarter wave resonators (QWR). Steering effects in QWRs over the period have also been studied. In one APF period, the individual phase of resonators changes sign resulting in a vertical steering kick in a particular direction, which is less as compared to the case where all the individual resonators operate in the same phase.

Alternate phase focusing in sequence of independent phased resonators as superconducting linac boosters

Post acceleration of ion beams would be done in Radio Frequency Quadrupole (RFQ) LINAC for the upcoming Radioactive Ion Beam (RIB) facility at Variable Energy Cyclotron Centre (VECC), India. A 33.7 Mhz RFQ capable of accelerating stable as well as RI beams of q/A≥1/16 to about 30 keV/u has already been constructed and operational since September 2005. This has been installed in a dedicated beam line for doing material science experiments. Another 3.4 m long RFQ resonating at 37.8 Mhz and capable of accelerating heavy ion beams upto 98 keV/u have been fabricated which is to be installed in the beam-line for the VEC-RIB facility. The physical parameters, rf test along with the measurements of accelerated beams from RFQ would be presented. DESIGN OF RFQ We plan to accelerate beams with mass ranging up to A=150 in the VEC-RIB facility[1]. The radioactive atoms would be ionized in Electron Cyclotron resonance ion source(ECRIS) operating in “High B-mode”. The ions would be then subsequently mass separated and accelerated in RFQ and Linac tanks[2]. ECRIS in principle would be able to deliver beams of around 15 for uranium even in the on-line mode .Thus q/A≥ 1/14 seems to be a judicious choice for our RFQ. Normalized emmittance of ion beam has been taken to be 0.05 π cm mrad. Characteristic radius of 0.71 mm for the RFQ ensured a good transmission of the RI beams through the RFQ. The four-rod type structure have extended vanes supported on posts similar to the structure developed by Fujisawa[3]. The rods are placed at an angle of 45 with respect to conventional horizontal and vertical axes. The beam dynamics simulation has been done using GENRFQ and PARMTEQ code. Optimization of different physical parameters was done keeping in mind the goal to achieve the desired acceleration with minimum vane length and maximum transmission efficiency. Initially the RFQ was decided to design for input beam of energy of 1keV/u and input bunch width of ±42 and final energy of 86 keV/u[4]. The RFQ was designed to resonate at frequency of 35 MHz. A half scale cold model was fabricated for RF measurements. The results show good agreement with the simulation using MAFIA. In the next stage we have designed and fabricated 33.7 MHz RFQ delivering beam of 29 keV/u to be installed in the dedicated beam line for material science experiments . As the first post accelerator, using the experience and expertise gathered with 33.7 MHz RFQ final 3.4 m RFQ accelerating RIB’s to 98 keV/u have been fabricated. 33.7 MHz RFQ Design Parameters The RFQ is designed for an input dc beam of 1.38 keV/u, q/A=1/ 16, and resonant frequency of 33.7 MHz. The intervane voltage has been chosen to be 45.9 kV, which is about 1.12 times the Kilpatric limit for cw operation. With the interelectrode potential of 45.9 kV the calculated output energy comes out to be 29.06 keV/u for a vane length of 1.552 m. The radial matching section consists of 6 rf cells, and a total of 119 cells are needed to reach the energy. The synchronous phase in the acceleration section is chosen to be −30°. The calculated transmission efficiency is 95.8% for a beam current of 1 mA. The optimized physical parameters are shown in Fig.1. Energy width of the beam at the exit of RFQ is ± 0.67 keV/u. Figure 1: Optimised physical parameters variation along length of 33.7 MHz RFQ. RF Analysis MAFIA estimates resonant frequency, Q, and Rp values for the structure with unmodulated electrodes of the same characteristic radius to be 35 MHz, 9830, and 174 kΩ respectively. The measured resonating frequency is 33.7 MHz. The Q value measured using pick ups under 99% power reflection method is 5200.The tuning range of the tuner has been measured to be 100 KHz. Beam Energy Measurement Low energy beam transport line from ECRIS to RFQ consists of einzel lens,90dipole for q/A selection and solenoid as matching element. The separation stage is designed for a dispersion of 1.84 cm. The ions are extracted from ECRIS at 1.38 keV/u. In the downstream MOP034 Proceedings of LINAC08, Victoria, BC, Canada Proton and Ion Accelerators and Applications 142 2C RFQs of RFQ a QQD configuration has been installed for energy measurement. The quadrupole and dipole magnet strengths are calculated using TRANSPORT for RFQ beam energy of 29.06 keV/u, as theoretically predicted by PARMTEQ. The 5.4 m long beamline is designed for dispersion of 1.9 cm. The magnetic strengths of the quadrupoles and the dipole magnet are tuned so as to achieve maximum beam current on the Faraday cup (with electron suppression) placed upstream of the dipole after the RFQ. The beam tests have been carried out using oxygen (O, O, O), nitrogen (N, N), and argon (Ar).Typical transmission efficiency for most of the beams is 85% & 80% respectively for un analyzed and analyzed beam[5]. A plot of beam current measured on Faraday cup before RFQ as a function of vane voltage measured pickup voltage, proportional to vane voltage is shown in Fig.2.The transmission falls drastically when the vane voltage is reduced to a value lower than roughly 86.6% of the voltage corresponding to maximum transmission, as expected for the chosen synchronous phase of −30°. Figure 2: Variation of beam current with vane voltage for 16 O 3+ beam. 37.8 MHz RFQ Design Parameters The RFQ has been designed for DC beams with input energy of 1.7 keV/u. The vane voltage of 53.7 kV accelerates the beam to energy of 98 keV/u over a length of 3.12m. This voltage is around 1.12 times of Killpatric Voltage of 47.65 kV. RFQ consists of 6 radial matching sections (RMS) and in all 147 cells. The potential formulation in the RMS is similar to that proposed by Yamada [6], where the focusing strength (B) obeys a sinusoidal variation over the length of RMS. The calculated efficiency for 1mA beam comes out to be ~96% The variation of the optimized physical parameters along the length of RFQ is shown in Fig 3.The minimum aperture radius is 4.1mm while the maximum modulation parameter is 1.388. Energy width of the output beam through the RFQ is around ± 0.3% of the final energy. Output beam distribution as calculated by PARMTEQ, both in longitudinal & transverse phase space is shown in Fig 4. Figure 3: Variation of optimised physical parameters along the length of RFQ. Figure 4: Longitudinal and transverse beam distribution at the exit of RFQ. RF Analysis The RF structure design was done using the code ANSYS. The resonant frequency, Q and Rp value 0 20 40 60 80 100 120 140 0 20 40 60 80 100 E En er gy (k eV /u ) Cell Number -90 -80 -70 -60 -50 -40 -30

Alok Chakrabarti

Papers

Decay measurements of 43K(β−)43Ca by HRS and TAS

Development of an analog phase shifter for particle accelerator control circuits

Energy dependence of exotic nuclei production cross sections by photofission reaction in GDR range

Alternate phase focusing in sequence of independent phased resonators as superconducting linac boosters

Heavy Ion Radio-Frequency Quadrupole LINAC for VEC-RIB Facility