Implantable medical devices (IMDs) are medically necessary devices embedded in a human body that monitor chronic disorders or automatically deliver therapies, such as insulin pumps or pacemakers. Typically, they are small form-factor devices with limited battery and processing power. Most IMDs have wireless capabilities that allow them to share data with an offboard programming device, such as a smartphone application, that has more storage and processing power than the IMD itself. Additionally, the programming device can send commands back to the IMD to change its settings according to the treatment plan. As such, wirelessly sharing information between an IMD and offboard device can help medical providers monitor the patient's health remotely while giving the patient more insight into their condition, more autonomy, and fewer in-person appointments. However, serious security concerns have arisen as researchers have demonstrated it is possible to hack these devices to obtain sensitive information or potentially harm the patient. This is particularly easy to do as most IMDs transmit their data in the clear to avoid allocating their limited resources to encrypting their packets. As these concerns and the percentage of the American population with IMDs grows, there is another fear that bad actors could exploit the link between the programming device and IMD. Theoretically, a hacker could launch a man in the middle attack to send the IMD unauthorized commands, reprogramming it to act as a radio, sniffing signals of interest in the environment. As such, the hacker could use the IMD as a software defined radio (SDR) that captures sensitive or even classified information without the patient's knowledge. If this were to happen, it is possible an unwitting person with an IMD who has access to classified or sensitive information could be used to exfiltrate data that, in the wrong hands, could be used for corporate espionage or to the detriment of national security. While governing bodies agree that cybersecurity risks are present in IMD systems, there are no requirements for IMD manufacturers to create their devices with security measures that mitigate these risks. Researchers have proposed physical, technical, and administrative security measures for IMDs, but other existing wireless security techniques may apply to the healthcare space and need to be explored. Beamforming is an array signal processing technique that relies on individual elements of antenna arrays adjusting their phase and amplitude to create an overall effect of directing RF energy in a particular direction. Similarly, cooperative beamforming uses several physically separate "friendly" beamforming-capable devices to collectively send artificial noise to eavesdroppers while ensuring the signal is successfully received by the intended receiver. Although there are several cooperative jamming algorithms, they share the underlying principles of minimizing SINR at potential eavesdroppers while maximizing the SINR at the intended receiver. Researchers exploring cooperative jamming have largely used models to estimate its impact on channel secrecy. While RF propagation and communication system modeling provides valuable insight into system performance, many theoretical and empirical models are limited by the extent to which the operational environment matches that of the model itself. Ray tracing, alternatively, is more widely applicable as it accounts for a 3D environment and the objects a signal interacts with in that space. A ray is defined as an individual RF signal that travels in a straight line through a uniform medium; obeys the laws of reflection, refraction, and diffraction; and carries energy. As the ray interacts with objects in the environment, its energy will decrease by some amount that depends on the materials and geometry of the object. While research has predominantly focused on applications like cellular communications, the same principles of minimizing SINR at potential eavesdroppers while maximizing the SINR at the intended receiver can be applied to IMDs. As IMD use cases assume the programmer is nearby, the friendly nodes will not need to act as relays and can instead focus all their power on jamming. The number of cooperative jammers will be low to simulate the number of devices an individual might have in a workspace or office setting, like a personal phone, smart watch, or laptop, and realistic power constraints will be observed. Further, ray tracing software will provide additional visual insights into how various building materials like drywall, concrete, brick, and glass impact cooperative jamming. Through these simulations, the trade-off between secrecy rate and physical separation and layout of friendly nodes can be determined, which in turn may inform how companies or individuals can protect their proprietary and personal information. / Master of Science / Implantable medical devices (IMDs) are medically necessary devices embedded in a human body that monitor chronic disorders or automatically deliver therapies, such as insulin pumps or pacemakers. The data on IMDs need to be processed and their settings might need to be adjusted, but IMDs themselves usually cannot support direct user input, such as through screens or buttons, as they are inaccessible without surgery or generally too small to have space for displays. Further, they lack processing power and battery life due to their small form-factors, so relatively little data remains onboard. Instead, it is more convenient for the IMDs to wirelessly send their data to a more powerful external device like a smartphone. Since smartphones have more battery and processing resources available, and are easily recharged, they can store more data, monitor trends in the patient's health records, and upload the data to a server which the doctors can access. Additionally, these devices can send commands back to the IMD to change its settings according to the treatment plan. As such, wirelessly sharing information between an IMD and offboard programming device can help medical providers monitor the patient's health remotely while giving the patient more insight into their condition, more autonomy, and fewer in-person appointments. However, serious security concerns have arisen as researchers have demonstrated it is possible to hack these devices to obtain sensitive information or potentially harm the patient. As these concerns and the percentage of the American population with IMDs grows, there is another fear that bad actors could exploit the link between the programming device and IMD. Theoretically, a hacker could send the IMD unauthorized commands that change the IMD's behavior so that they are reprogrammed to act as radios listening for signals in the environment in order to steal sensitive or even classified information. While governing bodies agree that cybersecurity risks are present in IMD systems, there are no requirements for IMD manufacturers to create their devices with security measures that mitigate these risks. Researchers have proposed physical, technical, and administrative security measures for IMDs, but other existing wireless security techniques may apply to the healthcare space and need to be explored. Cooperative jamming is an existing defensive wireless technique that reduces the likelihood of an eavesdropper gaining access to unauthorized information. A known set of "friendly" transmitters each transmit noise to eavesdroppers while ensuring the signal is successfully received by the intended receiver. Researchers exploring cooperative jamming have largely used models to estimate its impact on channel secrecy. While RF propagation and communication system modeling provides valuable insight into system performance, many theoretical and empirical models are limited by the extent to which the operational environment matches that of the model itself. Ray tracing, alternatively, is more widely applicable as it accounts for a 3D environment and the objects a signal interacts with in that space. A ray is defined as an individual RF signal that travels in a straight line through a uniform medium; obeys the laws of reflection, refraction, and diffraction; and carries energy. As the ray interacts with objects in the environment, its energy will decrease by some amount that depends on the materials and geometry of the object. Thus, using ray tracing to model cooperative jamming will provide new insights into the degree to which cooperative jamming could be used to protect an IMD from eavesdroppers, and how companies or individuals can protect their proprietary and personal information.

Univ., Diss.--Frankfurt a.M., 2000.

The present study was implemented using two different X-ray detection systems; a monochromatic X-ray system for X-ray Fluorescence (XRF) and Angular Dispersive X-ray Diffraction (ADXRD) techniques, and a combined Polarized Energy Dispersive X-ray Fluorescence (PEDXRF) and Energy Dispersive X-ray Diffraction (EDXRD) system. As both of these systems involve different techniques, the primary objective of this study was to evaluate the performance and accuracy of each system using results achieved from XRF measurements. The assessment of the two systems was carried out by investigating invasive ductal carcinoma (IDC) of breast and normal surrounding breast tissues. The results established from the two XRF systems are in a very good agreement with each other. The statistical analysis reveals a significant and measurable increase at P<0.01 in the concentration of K, Ca, Zn, Rb and Fe (P<0.05) in the tumor tissue when compared with the healthy tissue. However, the levels of Cl, Cu and Br attained by both systems have not demonstrated a statistically significant difference between the normal and cancerous tissues. Investigating the structural components of the same breast tissues using of the X-ray Diffraction (XRD) spectrometers incorporated in both systems indicated a statistically significant difference in the components of normal and malignant samples. Furthermore, the results have shown a remarkable increase in the fibrous and water contents of the tumour tissue at P<0.01, and a significant increase in the adipose content of the normal tissue at P<0.01. The results acquired from both XRD approaches were shown to be statistically compatible with each other. Overall, the comparisons between the two X-ray detection systems have shown tremendous results for the combined PEDXRF and EDXRD system for the purpose of classifying normal and tumor breast tissues. / Thesis / Master of Science (MSc)

The detection of γ-rays from explosive astrophysical scenarios such as novae provides an excellent opportunity for the study of on-going nucleosynthesis in the Universe. Within this context, this work has addressed an uncertainty in the destruction rate of the 18F nucleus, thought to be the primary source of 511 keV γ-rays from novae. A direct measurement of the 18F(p,α )15O cross section has provided the opportunity to extract resonance parameters through the R-Matrix formalism. The inferred parameters of populated states in 19Ne include the observation of a broad 1/2+ state, consistent with a recent theoretical prediction, which will have a significant impact on the rate of destruction of this γ-ray producing radioisotope. The 18O(p,α )15N reaction follows similar nuclear and kinematic processes and is expected to occur in the hydrogen burning layers of AGB stars. Resonance widths have been extracted from a direct measurement in the region around a poorly constrained broad state close to the Gamow window. This has produced a new parameter set for future reference and provides new information on the reaction rate. The complex R-Matrix formalism used in these analyses is a crucial tool in the study of nuclear astrophysics reactions, and many codes have been written to implement the complex mathematics. This thesis presents a comparison of two publicly available codes from the JINA collaboration and a code used extensively by the University of Edinburgh. For this, the recent results of the 18F destruction reaction, presented here, have been used. A minor error was found within one of the codes, and corrected. The final parameters extracted, and the resulting cross sections calculations, are shown to be consistent between the three codes. A further γ-ray line of interest at 1.809 MeV, characteristic of 26Al decay, has been observed throughout the interstellar medium. If, however, this isotope is formed in a known isomeric state, its decay bypasses the emission of this γ-ray, thus complicating the interpretation of observed γ-ray fluxes. To this end, an experiment has been carried out, providing proof of principle of a direct measurement of the 26mAl(p,γ)27Si reaction. The calculation of the isomeric intensity is presented here.

No description available.

Thesis. 1975. B.S. cn--Massachusetts Institute of Technology. Dept. of Physics. / MICROFICHE COPY AVAILABLE IN ARCHIVES. / Includes bibliographical references. / B.S.cn

Thesis (Ph. D.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 107-113). Also available on the World Wide Web.

The RS 2400 irradiator has been looked to as a replacement for discontinued gamma irradiators. The RS 2400 has a cylindrical, rather than point, x-ray source, which yields higher dose rates. The irradiator unit allows the user to set the current, voltage, and time for which the sample is to be irradiated, but gives no conversion between these values and the dose delivered. Working with Mississippi State University’s Experimental Seafood Processing Laboratory (ESPL), the purpose of this research was to characterize the dose delivered by the RS 2400 for typical operating conditions. The RS 2400 exposure rate increases, as expected, as the current and voltage are increased. The x-ray beam is uniform within 10% at the surface of the x-ray tube over a wide range of voltages, with the exception of the leftmost 5 cm of the tube, where structural supports are located. At the maximum operating parameters (150 kV and 45 mA), the beam has a first half value layer (HVL1) of 13.66 mm aluminum, a homogeneity coefficient of 0.47, and equivalent photon energy (hveq) of 88.5 keV. This suggests a broad energy x-ray beam. The maximum deliverable dose rate to tissue at the surface of the x-ray tube is 65 Gy min-1 ± 3.1%, but it is unlikely that any sample will ever be irradiated this close to the x-ray tube. The standard sample canisters are 7.62 cm in diameter and the maximum deliverable dose rate to tissue at the canister location (with no canister present) is 37 Gy min-1 ± 3.1%. This is similar to the 45 Gy min-1 value that Rad Source Technologies, Inc. gives for the irradiator. Irradiation of live oysters is of primary interest to the ESPL. For irradiation, oysters will most likely be placed in the 10.2 cm diameter plastic canisters since the 7.62 cm diameter canisters are not wide enough to hold larger oysters. The oyster shells and increased distance from the x-ray source reduce the maximum deliverable dose rate to 14.1 Gy min-1 ± 6.5% for thin-shelled oysters and 12.3 Gy min-1 ± 6.2% for thick-shelled oysters.

Thesis (M.S.)--University of Florida, 2003. / Title from title page of source document. Includes vita. Includes bibliographical references.

This thesis focuses on the radiation mechanisms of non-thermal X-rays and soft gamma-rays of two types of thousands year old spin-down powered pulsars. The thousands year old pulsars have distinct radiation behaviors from the middle-aged gamma-ray pulsars. In the magnetosphere of the pulsar, the particles are accelerated by the electric field resulting from the rotation of the neutron star. These accelerated particles move along the magnetic field lines and emit GeV gamma-ray curvature photons. For the middle-aged pulsars, most of the curvature photons, whose observed spectra are described well by power law with exponential cut-off, can escape out of the light cylinder. In X-ray band, the middle-aged pulsars usually have black body radiation with a weak non-thermal component described by power law. On the other hand, for the thousands-year-old pulsars, the curvature spectra in GeV band, which obey power law with exponential cut-off, are smeared out by the pair creation or missed by the line of sight. The secondary pairs generated by pair creation processes spiral around the magnetic field lines and emit synchrotron photons, and the young pulsars have stronger non-thermal X-ray and soft gamma-ray radiation than the middle-aged ones. Seven young pulsars have been studied here, they are the Crab pulsar, PSRs B0540-69, B1509-58, J1846-0258, J1811-1925, J1617-5055 and J1930+1852. These seven fall into two categories: the Crab-like pulsars and soft gamma-ray pulsars. The Crab-like pulsars include the Crab pulsar and the Giant Crab PSR B0540-69, and the soft gamma-ray pulsars include the other five. The main difference between the two types of young pulsars is that the Crab-like pulsars’ spectra peak at E ≤ 1MeV while the soft gamma-ray pulsars’ spectra (in units of MeV/cm2/s) peak at E ∼ 10MeV. Their spectra also have different photon indices in X-ray band. The physics behind is two different pair creations, the photon-photon pair creation and the magnetic pair creation. The former happens when a high energy photon collides with a soft photon, and the latter happens when a high energy photon penetrates through strong perpendicular magnetic field. In the outer gap of the pulsar, a large mount of pairs are generated around the null charge surface via photon-photon pair creation, and the electric field separates the two charges to move in opposite directions. Therefore, there are outflow and inflow of particles in the magnetosphere, whose curvature photons are converted to pairs by photon-photon pair creation and magnetic pair creation respectively. For the Crab-like pulsar, the non-thermal X-rays and soft gamma-rays are emitted by the outgoing secondary pairs generated by photon-photon pair creation in the outer magnetosphere; for the soft gamma-ray pulsar, the radiating secondary pairs are generated below the null charge surface by the magnetic pair creation. / published_or_final_version / Physics / Doctoral / Doctor of Philosophy