71 research outputs found
Anisotropic optical properties of Fe/GaAs(001) nanolayers from first principles
We investigate the anisotropy of the optical properties of thin Fe films on
GaAs(001) from first-principles calculations. Both intrinsic and
magnetization-induced anisotropy are covered by studying the system in the
presence of spin-orbit coupling and external magnetic fields. We use the
linearized augmented plane wave method, as implemented in the WIEN2k density
functional theory code, to show that the symmetric anisotropy of the
spin-orbit coupling fields at the Fe/GaAs(001) interface manifests itself in
the corresponding anisotropy of the optical conductivity and the polar
magneto-optical Kerr effect. While their magnetization-induced anisotropy is
negligible, the intrinsic anisotropy of the optical properties is significant
and reflects the underlying symmetry of the Fe/GaAs(001) interface.
This suggests that the effects of anisotropic spin-orbit coupling fields in
experimentally relevant Fe/GaAs(001) slabs can be studied by purely optical
means.Comment: 8 pages, 11 figure
Optical conductivity of hydrogenated graphene from first principles
We investigate the effect of hydrogen coverage on the optical conductivity of
single-side hydrogenated graphene from first principles calculations. To
account for different degrees of uniform hydrogen coverage we calculate the
complex optical conductivity for graphene supercells of various sizes, each
containing a single additional hydrogen atom. We use the linearized augmented
plane wave (LAPW) method, as implemented in the WIEN2k density functional
theory code, to show that the hydrogen coverage strongly influences the complex
optical conductivity and thus the optical properties, such as absorption, of
hydrogenated graphene. We find that the optical conductivity of graphene in the
infrared, visible, and ultraviolet range has different characteristic features
depending on the degree of hydrogen coverage. This opens up new possibilities
to tailor the optical properties of graphene by reversible hydrogenation, and
to determine the hydrogen coverage of hydrogenated graphene samples in the
experiment by contact-free optical absorption measurements.Comment: 8 pages, 7 figure
Optical properties of hydrogenated graphene and Fe/GaAs(001) from first principles
Hydrogenated graphene and the Fe/GaAs(001) heterostructure are candidate systems for novel graphene- and semiconductor-based spintronics devices. This dissertation investigates the optical properties of these systems from first-principles density functional theory (DFT) calculations. Its goal is to motivate the use of optical methods in the experimental study of hydrogenated graphene and Fe/GaAs(001).
Indeed, the results suggest that optical methods can be used to study important properties of these systems, such as the effects of the spin-orbit coupling fields at the Fe/GaAs interface. A better understanding of those can help advance the design of efficient spin injection devices. Other interesting properties that can be studied by optical methods are the hydrogenation-induced band gap and magnetism in graphene. Eventually, this could lead to graphene-based spin manipulation devices such as graphene transistors.
In addition to these results a lot of background on ab initio DFT is covered, as well as the theory explaining the anisotropic polar magneto-optical Kerr effect (AP-MOKE)
Spin-orbit coupling in fluorinated graphene
We report on theoretical investigations of the spin-orbit coupling effects in
fluorinated graphene. First-principles density functional calculations are
performed for the dense and dilute adatom coverage limits. The dense limit is
represented by the single-side semifluorinated graphene, which is a metal with
spin-orbit splittings of about 10 meV. To simulate the effects of a single
adatom, we also calculate the electronic structure of a
supercell, with one fluorine atom in the top position. Since this dilute limit
is useful to study spin transport and spin relaxation, we also introduce a
realistic effective hopping Hamiltonian, based on symmetry considerations,
which describes the supercell bands around the Fermi level. We provide the
Hamiltonian parameters which are best fits to the first-principles data. We
demonstrate that, unlike for the case of hydrogen adatoms, fluorine's own
spin-orbit coupling is the principal cause of the giant induced local
spin-orbit coupling in graphene. The hybridization induced transfer of
spin-orbit coupling from graphene's bonds, important for hydrogenated
graphene, contributes much less. Furthermore, the magnitude of the induced
spin-orbit coupling due to fluorine adatoms is about times more than
that of pristine graphene, and 10 times more than that of hydrogenated
graphene. Also unlike hydrogen, the fluorine adatom is not a narrow resonant
scatterer at the Dirac point. The resonant peak in the density of states of
fluorinated graphene in the dilute limit lies 260 meV below the Dirac point.
The peak is rather broad, about 300 meV, making the fluorine adatom only a
weakly resonant scatterer.Comment: 11 pages, 14 figure
Diagnostic Utility of Temporal Muscle Thickness as a Monitoring Tool for Muscle Wasting in Neurocritical Care
Temporalis muscle (TM) atrophy has emerged as a potential biomarker for muscle wasting. However, its diagnostic utility as a monitoring tool in intensive care remains uncertain. Hence, the objective of this study was to evaluate the diagnostic value of sequential ultrasound- and computed tomography (CT)-based measurements of TM thickness (TMT). With a prospective observational design, we included 40 patients without preexisting sarcopenia admitted to a neurointensive care unit. TMT measurements, performed upon admission and serially every 3–4 days, were correlated with rectus femoris muscle thickness (RFT) ultrasound measurements. Interrater reliability was assessed by Bland Altmann plots and intraclass correlation coefficient (ICC). Analysis of variance was performed in subgroups to evaluate differences in the standard error of measurement (SEM). RFT decline was paralleled by ultrasound- as well as CT-based TMT measurements (TMT to RFT: r = 0.746, p < 0.001; CT-based TMT to ultrasound-based RFT: r = 0.609, p < 0.001). ICC was 0.80 [95% CI 0.74, 0.84] for ultrasound-based assessment and 0.90 [95% CI 0.88, 0.92] for CT-based TMT measurements. Analysis of variance for BMI, Heckmatt score, fluid balance, and agitation showed no evidence of measurement errors in these subgroups. This study demonstrates the clinical feasibility and utility of ultrasound- and CT-based TMT measurements for the assessment of muscle wasting
Advanced Materials Technologies / 3D Printing of Hierarchical Porous Silica and -Quartz
The ability to macroscopically shape highly porous oxide materials while concomitantly tailoring the porous network structure as desired by simple and environmentally friendly processes is of great importance in many fields. Here, a purely aqueous printing process toward deliberately shaped, hierarchically organized amorphous silica and the corresponding polycrystalline quartz analogues based on a direct ink writing process (DIW) is presented. The key to success is the careful development of the solgel ink, which is based on an acidic aqueous sol of a glycolated silane and structuredirecting agents. The resulting 3D (DIW) printed silica consists of a macroporous network of struts comprising hexagonally arranged mesopores on a 2D hexagonal lattice. Together with a printed porous superstructure on the millimeter scale, welldefined pore sizes and shapes on at least three hierarchy levels can thus be fabricated. The introduction of devitrifying agents in the printed green part and subsequent heat treatment allows for the transformation of the silica structure into polycrystalline quartz. While small pores (micro and mesopores below 10 nm) are lost, the printed morphology and the macroporous network of struts is preserved during crystallization.1605N20(VLID)266643
Benchmarking ChatGPT-4 on ACR Radiation Oncology In-Training (TXIT) Exam and Red Journal Gray Zone Cases: Potentials and Challenges for AI-Assisted Medical Education and Decision Making in Radiation Oncology
The potential of large language models in medicine for education and decision
making purposes has been demonstrated as they achieve decent scores on medical
exams such as the United States Medical Licensing Exam (USMLE) and the MedQA
exam. In this work, we evaluate the performance of ChatGPT-4 in the specialized
field of radiation oncology using the 38th American College of Radiology (ACR)
radiation oncology in-training (TXIT) exam and the 2022 Red Journal gray zone
cases. For the TXIT exam, ChatGPT-3.5 and ChatGPT-4 have achieved the scores of
63.65% and 74.57%, respectively, highlighting the advantage of the latest
ChatGPT-4 model. Based on the TXIT exam, ChatGPT-4's strong and weak areas in
radiation oncology are identified to some extent. Specifically, ChatGPT-4
demonstrates good knowledge of statistics, CNS & eye, pediatrics, biology, and
physics but has limitations in bone & soft tissue and gynecology, as per the
ACR knowledge domain. Regarding clinical care paths, ChatGPT-4 performs well in
diagnosis, prognosis, and toxicity but lacks proficiency in topics related to
brachytherapy and dosimetry, as well as in-depth questions from clinical
trials. For the gray zone cases, ChatGPT-4 is able to suggest a personalized
treatment approach to each case with high correctness and comprehensiveness.
Most importantly, it provides novel treatment aspects for many cases, which are
not suggested by any human experts. Both evaluations demonstrate the potential
of ChatGPT-4 in medical education for the general public and cancer patients,
as well as the potential to aid clinical decision-making, while acknowledging
its limitations in certain domains. Because of the risk of hallucination, facts
provided by ChatGPT always need to be verified
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