Kvazielastično raspršenje elektrona na 4He između 328 i 725 MeV

4He(e,e˘) cross section data at 328, 365 and 725 MeV have been analyzed using the quasi-free scattering (QFS) model of Lightbody and O\u27Connell. The QFS model provides an improved description of the shape and magnitude of the cross section data when compared with plane-wave impulse approximation calculations, particularly at higher values of the electron energy loss. Although the nucleon separation energy is about 20 MeV in 4He, the best QFS results are obtained for a 6 MeV value.Podaci za udarni presjek 4He na energijama od 328, 365 i 725 MeV analizirani su koristeći model kvazi-slobodnog raspršenja Lightbodyja i O\u27Connella. Model omogućava poboljšan opis oblika i iznosa udarnog presjeka u odnosu na rezultate dobivene u aproksimaciji impulsa ravnih valova. To naročito vrijedi za veće gubitke energije elektrona. Iako je energija separacije oko 20 MeV u 4He, najbolji rezultati dobiveni su za 6 MeV-a

Radiotherapy Dose Optimization in Target Tissues Using Internal Radiation-Generating Devices and Microspheres

Preferentially delivering ionizing radiation to target tissues during radiotherapy procedures is investigated using internal radiation-generating devices and microspheres loaded with radioactive material. This chapter presumes the existence of internal radiation-generating devices and develops their requisite characteristics to permit the selective irradiation of tumors. The feasibility of disrupting a tumor’s vascular structure is also investigated. Calculated absorbed dose profiles for both approaches demonstrate that dose can be successfully localized in a target tissue while minimizing the delivery to healthy tissue

Izrazi za zakrivljenost u općoj teoriji relativnosti

A clear physical description of a variety of spacetime geometries is provided in terms of the various connection coefficients and curvature-related tensors. The affine connection coefficients, the Riemann curvature tensor, Ricci tensor, scalar curvature and Einstein tensor, and associated discussion is provided for flat spacetime, the Schwarzschild geometry, the Morris-Thorne wormhole geometry, the FriedmannRobertson-Walker geometry, and a static spherical geometry.Daje se jasan opis niza prostorno-vremenskih geometrija preko veznih koeficijenata i tenzora zakrivljenosti koji se rabe u teoriji. Navode se afini vezni koeficijenti, Riemannov tenzor zakrivljenosti, Riccijev tenzor, skalarna zakrivljenost i Einsteinov tenzor, i oni se raspravljaju za ravan prostor, Schwarzschildovu geometriju, MorrisThorneovu geometriju crvotočina, te Friedmann-Robertson-Walkerovu i statičku sfernu geometriju

Nastanak centripetalnog ubrzanja u Frenet–Serretovom sustavu

A clear physical description of a particle\u27s motion in terms of the components of its acceleration is obtained if the trajectory is described in terms of the Frenet-Serret frame. Within this frame, centripetal acceleration emerges as a natural consequence of a particle\u27s motion.Ako se putanja čestice opisuje u Frenet–Serretovom sustavu, postiže se jasan fizički opis njenog gibanja preko komponenata njenog ubrzanja. U tom se sustavu centripetalno ubrzanje javlja kao prirodna posljedica gibanja čestice

Solar System Planets and Exoplanets

Solar System planets have been studied for centuries, but the observation of exoplanets is only a few decades old. Consequently, knowledge of exoplanets is considerably more limited than Solar System planets. This chapter reviews the essential characteristics of Solar System planets and associated data derived from a variety of observational approaches. Exoplanet characteristics and their comparison to Solar System planets are provided as well as general detection methods and planned probes to gather additional data

How Reactivation of SARS-CoV-2 in Astronauts with Dysregulated Immune Systems Can Negatively Affect the Odds of Success in Future Space Missions

We have previously reported that during future space missions the risk of severe COVID-19 infection will be a cardinal issue that needs careful attention. Our studies show that even with the most reliable pre-mission screening and quarantine strategies, astronauts with a latent (hidden, inactive, or dormant) SARS-CoV-2 infection might be sent to space. Given this consideration, an asymptomatic individual with dormant SARS-CoV-2 infection may successfully pass all the pre-launch medical tests. Then during a space mission such as a journey to Mars or beyond, when the immune system of these astronauts starts to weaken, the dormant infection may progress to a severe infection that possibly affects the chance of the mission’s success. The effects of microgravity and the elevated space radiation are two key factors that should be evaluated. Furthermore, the limited size of the spacecraft, the proximity of crew members during flight operations, spacecraft atmospheric composition, limited exercise capability, effects of viral response to space radiation, and uncertainty in the likelihood of the virus to mutate and evolve during a space mission merit additional study