A gas attenuator is an important element of the LCLS facility. The attenuator must operate in a broad range of x-ray energies, provide attenuation coefficient between 1 and 10 with the accuracy of 1% and, at the same time, be reliable and allow for many months of un-interrupted operation. S. Shen [1] has recently carried out a detailed design study of the attenuator based on the use of nitrogen...

In this paper, a 4-bit digital step attenuator using 0.25 μm GaN HEMT technology for wideband radar systems is presented. A switched-path topology with resistive T-type attenuators and double-pole double-throw (DPDT) switches was used to achieve both low insertion loss phase/amplitude error. The measured of the reference state 2.8–8.3 dB at DC-12 GHz. input output return are less than 12 An att...

Two mechanisms account for AmpC activity in Escherichia coli, namely, mutations in the ampC promoter and attenuator regions resulting in ampC overexpression and acquisition of plasmid-carried ampC genes. In this study, we analyzed 51 clinical E. coli isolates with reduced susceptibility to amoxicillin-clavulanic acid, piperacillin-tazobactam, or extended-spectrum cephalosporins for the presence...

Nuclear Regulatory Commission (NRC) guidelines state that dose calibrators must be tested for linearity upon installation and quarterly thereafter over a range of activities from 10 ~J,Ci (370 kBq) to the highest dose administered to the patient (300 mCi [11.1 GBq] ofiodine-131 for therapy at our institution). The simplest method of linearity testing utilizes commercial attenuator kits. These k...

...............................................................................................1 Chapter 1: Gravitational Waves & LIGO.......................................................2 1.1 Gravitational Waves.....................................................................2 1.2 LIGO......................................................................................2 1.3 A Source of ...

We examined the dose distributions generated by Pinnacle3 (Philips Radiation Oncology Systems, Milpitas, CA) for intensity-modulated radiotherapy (IMRT) plans using a cubic-block-piled compensator as the intensity modulator for 4-MV and 10-MV photon beams. The Pinnacle treatment planning system (TPS) uses an algorithm in which only the physical density of the absorber is required for calculatin...

This study describes the importance of attenuator scatter in the construction of compensators. The attenuator used in this study was Lipowitz metal, commonly referred to as cerrobend. Linear attenuation coefficients of cerrobend were measured in air for different thickness of cerrobend sheets and different field sizes for a 6-MV photon beam. The magnitude of the dose contribution from photons s...

The interference effects caused by the Fresnel reflections of a Gaussian beam on the boundaries of a dielectric plate, which can be considered as a Fabry-Perot etalon, were theoretically and experimentally investigated. In addition to the incident angle and the polarization of the incident light, two additional parameters--the plate's parallelism and the temperature--which are often neglected, ...