COMPTEL neutron response at 17 MeV

The Compton imaging telescope (COMPTEL) instrument of the Gamma Ray Observatory was exposed to 17 MeV d,t neutrons prior to launch. These data were analyzed and compared with Monte Carlo calculations using the MCNP(LANL) code. Energy and angular resolutions are compared and absolute efficiencies are calculated at 0 and 30 degrees incident angle. The COMPTEL neutron responses at 17 MeV and higher energies are needed to understand solar flare neutron data

Nonlocal density functionals and the linear response of the homogeneous electron gas

The known and usable truly nonlocal functionals for exchange-correlation energy of the inhomogeneous electron gas are the ADA (average density approximation) and the WDA (weighted density approximation). ADA, by design, yields the correct linear response function of the uniform electron gas. WDA is constructed so that it is exact in the limit of one-electron systems. We derive an expression for the linear response of the uniform gas in the WDA, and calculate it for several flavors of WDA. We then compare the results with the Monte-Carlo data on the exchange-correlation local field correction, and identify the weak points of conventional WDA in the homogeneous limit. We suggest how the WDA can be modified to improve the response function. The resulting approximation is a good one in both opposite limits, and should be useful for practical nonlocal density functional calculations.Comment: 4 pages, two eps figures embedde

Detecting Intra-Fraction Motion in Patients Undergoing Radiation Treatment Using a Low-Cost Wireless Accelerometer

The utility of a novel, high-precision, non-intrusive, wireless, accelerometer-based patient orientation monitoring system (APOMS) in determining orientation change in patients undergoing radiation treatment is reported here. Using this system a small wireless accelerometer sensor is placed on a patient’s skin, broadcasting its orientation to the receiving station connected to a PC in the control area. A threshold-based algorithm is developed to identify the exact amount of the patient’s head orientation change. Through real-time measurements, an audible alarm can alert the radiation therapist if the user-defined orientation threshold is violated. Our results indicate that, in spite of its low-cost and simplicity, the APOMS is highly sensitive and offers accurate measurements. Furthermore, the APOMS is patient friendly, vendor neutral, and requires minimal user training. The versatile architecture of the APOMS makes it potentially suitable for variety of applications, including study of correlation between external and internal markers during Image-Guided Radiation Therapy (IGRT), with no major changes in hardware setup or algorithm

Assessment of Crestal Bone Loss and Implant Stability of Implant Drilling Protocol at Low Speed without Irrigation versus Conventional Drilling Protocol

Abstract Aim: This study assesses crestal bone loss surrounding dental implants, primary and secondary stability in sites prepared by conventional versus low speed drilling protocol. Material and Methods: Ten patients received 20 implants to restore an edentulous area in the lower posterior mandibular area. Patients were blindly divided into a control and study group. In the control group, sequential drilling was performed at 1,200 rpm and torque of 30 Ncm with irrigation till reaching the planned length and diameter. In the Study group, sequential drilling was performed at 150 rpm and torque of 50 Ncm without irrigation till reaching the planned length and diameter. Digital periapical radiographs were taken immediately postoperative, after 3 and 6 months to assess the crestal bone loss. Osstell® was used to quantify the implant stability; the primary stability was measured right after implant placement and the secondary stability was assessed after 3 months. Results: There was no statistically significant difference in crestal bone loss between both groups. The results of the primary stability of the control group showed a greater value than that of the study group with a statistically significant difference, while there was no statistically significant difference in the secondary stability between groups. Conclusion: Within the limitations of this study, drilling at low speed without irrigation is a successful implant site preparation technique for dental implants