Production of x-rays
Damian Tolan, Rachel Hyland, Christopher Taylor, Arnold Cowen in Get Through, 2020
True.False – it is limited by peak instantaneous power delivery at the anode surface and the maximum anode surface temperature which results. This is largely set by the peak value of the voltage waveform.True – this can be calculated from the average power delivered over the exposure time, plus the influence of anode cooling processes. Therefore it is the average (or effective) kilovoltage, and not peak kV, which becomes significant.True – cooling the tube using active circulation of oil in the tube housing and air conditioning improves heat dissipation from the anode by cooling the x-ray tube housing. The anode also tends to have a larger mass to allow greater heat storage.False – because of the enormous amount of heat generated by the long exposures used in spiral scanning for volume acquisition, the anodes must have a rating of several million heat units.
Quality Control of High-Energy External Beams
W. P. M. Mayles, A. E. Nahum, J.-C. Rosenwald in Handbook of Radiotherapy Physics, 2021
Some older kilovoltage x-ray units and cobalt-60 units were controlled by a timer rather than by a transmission dosimeter. Modern kV units have transmission monitor chambers, except for those operating at low kV. Usually, the dose rate will take a finite time to stabilise, so that the dose delivered in 1 min will in general differ from the dose rate in mid-exposure. This difference is called the timer end error (see Section 10.4.2) or in the case of cobalt units, the source-transit time (see Section 12.4). Two approaches to the measurement of this correction are possible. In the dual exposure method, the output dose is measured first for 1 min and then for 2 min. The instantaneous dose rate is then the difference between the two readings, and the timer correction is the difference between the instantaneous dose rate (in cGy min−1) and the dose measured for a 1 min exposure. In the second method, the beam is first turned on, and then the dose delivered in a fixed period is measured using the start and stop buttons on the electrometer.
Low Energy Particle Accelerators and Laboratories
Vlado Valković in Low Energy Particle Accelerator-Based Technologies and Their Applications, 2022
Following products are supplied by HVEE:Ion accelerators: air insulated accelerators up to incl. 500 kV.Singletron single-ended accelerators up to incl. 6.0 MV (8.0 MV).Tandetron tandem accelerators up to incl. 6.0 MV (8.0 MV), DC as well as pulsed beams.Electron accelerators: beam energies up to incl. 6.0 MV (8.0 MV), beam power up to incl. 50 kW.
Importance of dosimetry protocol for cell irradiation on a low X-rays facility and consequences for the biological response
Published in International Journal of Radiation Biology, 2018
Morgane Dos Santos, Vincent Paget, Mariam Ben Kacem, François Trompier, Mohamed Amine Benadjaoud, Agnès François, Olivier Guipaud, Marc Benderitter, Fabien Milliat
Concerning determination of the beam quality specification, so of the KQ factor, it has long been known that the usual quantities are the kilovoltage (kV) generating potential and the half-value layer (HVL) determined in copper or aluminum (mm) (IAEA 2000). For each HV used with our SARRP, the corresponding HVL value was measured by following as closely as possible the method described in Protocols used for implementation of dosimetry on SARRP of the AAPM protocol (Ma et al. 2001). As the distance of 1 meter between the irradiation source and the detector cannot be achieved with the SARRP, we chose a distance of 70 cm for the measurements, thanks to which we are able to determine with accuracy the calibrated factor for each HT and filtration used on the SARRP. Calibration factors of each ionization chamber were also measured following the AAPM protocol.
The force-from-lipid principle and its origin, a ‘what is true for E. coli is true for the elephant’ refrain
Published in Journal of Neurogenetics, 2022
FFL’s broad implication is best illustrated by the well-known voltage-dependent K+ channel, Kv. Kv’s opening tendency is much higher in the tensed membrane than it is in membrane constrained by cytoskeleton (Morris, Prikryl, & Joos, 2015; Schmidt, del Marmol, & MacKinnon, 2012). Channel opening by depolarization not only entails work done to move the S1-S4 peripheral domain, detaching it from the S5-S6 core, but also the work done to move the surrounding annular lipids, which is subjected to the innate as well as applied tension. The free-energy change associated with the bilayer deformation is comparable to that of the voltage-dependent part of the total gating energy (Reeves et al., 2008). Thus, Kv is as much a mechanosensitive as a voltage-sensitive channel (Schmidt et al., 2012). Nav, Cav, and TRPs, having the same design as Kv, should behave similarly (Anishkin, Loukin, Teng, & Kung, 2014). The ligand gated NMDA receptor channel also exhibits mechanosensitivity upon reconstitution into liposomes and activation either by membrane tension or arachidonic acid acting as an amphipath (Johnson, Battle, & Martinac, 2019; Kloda, Lua, Hall, Adams, & Martinac, 2007; Maneshi et al., 2017).
An improved surface for enhanced stem cell proliferation and osteogenic differentiation using electrospun composite PLLA/P123 scaffold
Published in Artificial Cells, Nanomedicine, and Biotechnology, 2018
Gebremariam Birhanu, Hamid Akbari Javar, Ehsan Seyedjafari, Ali Zandi-Karimi, Mehdi Dusti Telgerd
PLLA and PLLA–P123 composite (PLLA–P123) scaffolds were prepared by electrospinning as follows. To make PLLA scaffolds first, 0.43 g of PLLA was dissolved in 6 ml of chloroform and continuously stirred under magnetic stirrer at 200 rpm till all the PLLA was completely dissolved. For PLLA–P123 scaffolds 0.043 g of P123 was added with PLLA at the same time. After that 1 ml of DMF was added and stirred until bubble free transparent solution was formed and then transferred to two 5 cc syringe with needle. One-step two nozzles electrospinning was used to fabricate the scaffolds. The electrospinning experimental setup was a Nano Model (Tehran, Iran) with two nozzles. The voltage applied at the tip of the needle was 18 kV. The mass flow rates was 0.5 ml/h, and distance between the tip of the needle and the collector was maintained at 15 cm. The speed of the rotary collector was 400 rpm and scanning distance was 10 cm. To compare effect of P123 on the hydrophilicity of the scaffolds one group of PLLA electrospun nano fibrous scaffolds were air plasma treated with Diener electronic plasma cleaner (Germany).
Related Knowledge Centers
- Action Potential
- Membrane Potential
- Potassium Channel
- Voltage-Gated Ion Channel
- Shaker
- Kv1.1
- Kcna2
- Kcna3
- Kcna5
- Kcna6