1,159 research outputs found
Ab initio calculations of edge-functionalized armchair graphene nanoribbons: Structural, electronic, and vibrational effects
We present a theoretical study on narrow armchair graphene nanoribbons
(AGNRs) with hydroxyl functionalized edges. Although this kind of passivation
strongly affects the structure of the ribbon, a high degree of edge
functionalization proves to be particularly stable. An important consequence of
the geometric deviations is a severe reduction of the band-gap of the
investigated 7-AGNR. This shift follows a linear dependence on the number of
added hydroxyl groups per unit cell and thus offers the prospect of a tunable
band-gap by edge functionalization. We furthermore cover the behavior of
characteristic phonons for the ribbon itself as well as fingerprint modes of
the hydroxyl groups. A large down-shift of prominent Raman active modes allows
the experimental determination of the degree of edge functionalization.Comment: 6 pages, 9 figure
Thrombotic Thrombocytopenic Purpura Induced by Acute Pancreatitis
Thrombotic thrombocytopenic purpura (TTP) is a rare blood disorder characterized by clotting in small blood vessels of the body (microthrombi), resulting in a low platelet count. The disease consists of the pentad of microangiopathic hemolytic anemia, thrombocytopenic purpura, neurologic abnormalities, fever and renal disease. Many symptoms could develop with acute pancreatitis but being able to differentiate when it is associated with any hematological conditions such as TTP is crucial to initiate a proper medical treatment. We present a rare case of a thirty-eight years old African American female, who presented to the Emergency department with an abdominal pain associated with a pancreatic condition. A vital piece in medical practice is recognizing lifesaving decisions in critical conditions cases. Acute Pancreatitis (AP) is a well-described consequence of TTP but acute pancreatitis triggering TTP is still not as frequent
Analysis of the Surface Density and Reactivity of Perfluorophenylazide and the Impact on Ligand Immobilization
Perfluorophenylazide (PFPA) chemistry is a novel method for tailoring the surface properties of solid surfaces and nanoparticles. It is general and versatile, and has proven to be an efficient way to immobilize graphene, proteins, carbohydrates, and synthetic polymers. The main thrust of this work is to provide a detailed investigation on the chemical composition and surface density of the PFPA tailored surface. Specifically, gold surfaces were treated with PFPA-derivatized (11-mercaptoundecyl) tetra(ethylene glycol) (PFPA-MUTEG) mixed with 2-[2-(2-mercaptoethoxy)ethoxy]ethanol (MDEG) at varying solution mole ratios. Complementary analytical techniques were employed to characterize the resulting films including Fourier transform infrared spectroscopy to detect fingerprints of the PFPA group, x-ray photoelectron spectroscopy and ellipsometry to study the homogeneity and uniformity of the films, and near edge x-ray absorption fine structures to study the electronic and chemical structure of the PFPA groups. Results from these studies show that the films prepared from 90:10 and 80:20 PFPA-MUTEG/MDEG mixed solutions exhibited the highest surface density of PFPA and the most homogeneous coverage on the surface. A functional assay using surface plasmon resonance with carbohydrates covalently immobilized onto the PFPAmodified surfaces showed the highest binding affinity for lectin on the PFPA-MUTEG/MDEG film prepared from a 90:10 solution
An in-situ synchrotron XAS methodology for surface analysis under high temperature, pressure and shear
The complex tribochemical nature of lubricated tribological contacts is inaccessible in real time without altering their initial state. To overcome this issue, a new design of a pin-on-disc tribological apparatus was developed and combined with synchrotron X-ray absorption spectroscopy (XAS). Using the designed apparatus, it is possible to study in situ the transient decomposition reactions of various oil additives on different surfaces under a wide range of realistic operating conditions of contact pressure (1.0–3.0 GPa), temperature (25–120 °C), and sliding speed (30–3000 rpm or 0.15–15 m/s). To test the apparatus, several tribological tests were performed at different shearing times ranging from 2.5 to 60 min. These tests were carried out under helium atmosphere at a temperature of 80  °C, contact pressure of 2.2 GPa, and sliding speed of 50 rpm. The XAS experiments indicate that the zinc dialkyldithiophosphate antiwear additive decomposes in the oil to form a tribofilm on the iron surface at different reaction kinetics from the ones of the thermal film. The tribofilm composition evolves much faster than the one of the thermal film, which confirms that the formation of the tribofilm is a thermally activated process similar to the one of the thermal film but accelerated by shear. Furthermore, the results indicate that the sulfur of the formed film, whether a tribofilm or a thermal film, appears initially in the form of sulfate, with some sulfide, which under heat or shear is reduced into mainly sulfide
Raman and nuclear magnetic resonance investigation of alkali metal vapor interaction with alkene-based anti-relaxation coating
The use of anti-relaxation coatings in alkali vapor cells yields substantial
performance improvements by reducing the probability of spin relaxation in wall
collisions by several orders of magnitude. Some of the most effective
anti-relaxation coating materials are alpha-olefins, which (as in the case of
more traditional paraffin coatings) must undergo a curing period after cell
manufacturing in order to achieve the desired behavior. Until now, however, it
has been unclear what physicochemical processes occur during cell curing, and
how they may affect relevant cell properties. We present the results of
nondestructive Raman-spectroscopy and magnetic-resonance investigations of the
influence of alkali metal vapor (Cs or K) on an alpha-olefin, 1-nonadecene
coating the inner surface of a glass cell. It was found that during the curing
process, the alkali metal catalyzes migration of the carbon-carbon double bond,
yielding a mixture of cis- and trans-2-nonadecene.Comment: 5 pages, 6 figure
Inelastic electron tunneling via molecular vibrations in single-molecule transistors
In single-molecule transistors, we observe inelastic cotunneling features
that correspond energetically to vibrational excitations of the molecule, as
determined by Raman and infrared spectroscopy. This is a form of inelastic
electron tunneling spectroscopy of single molecules, with the transistor
geometry allowing in-situ tuning of the electronic states via a gate electrode.
The vibrational features shift and change shape as the electronic levels are
tuned near resonance, indicating significant modification of the vibrational
states. When the molecule contains an unpaired electron, we also observe
vibrational satellite features around the Kondo resonance.Comment: 5 pages, 4 figures. Supplementary information available upon reques
Infrared study of spin crossover Fe-picolylamine complex
Infrared (IR) absorption spectroscopy has been used to probe the evolution of
microscopic vibrational states upon the temperature- and photo-induced spin
crossovers in [Fe(2-picolylamine)3]Cl2EtOH (Fe-pic). To overcome the small
sizes and the strong IR absorption of the crystal samples used, an IR
synchrotron radiation source and an IR microscope have been used. The obtained
IR spectra of Fe-pic show large changes between high-spin and low-spin states
for both the temperature- and the photo- induced spin crossovers. Although the
spectra in the temperature- and photo-induced high-spin states are relatively
similar to each other, they show distinct differences below 750 cm-1. This
demonstrates that the photo-induced high-spin state involves microscopically
different characters from those of the temperature-induced high-spin state. The
results are discussed in terms of local pressure and structural deformations
within the picolylamine ligands, and in terms of their possible relevance to
the development of macroscopic photo-induced phase in Fe-pic.Comment: 6 pages (text) and 6 figures,submitted to J. Phys. Soc. Jp
Parker/buoyancy instabilities with anisotropic thermal conduction, cosmic rays, and arbitrary magnetic field strength
We report the results of a local stability analysis for a magnetized,
gravitationally stratified plasma containing cosmic rays. We account for
cosmic-ray diffusion and thermal conduction parallel to the magnetic field and
allow beta to take any value, where p is the plasma pressure and B is the
magnetic field strength. We take the gravitational acceleration to be in the
-z-direction and the equilibrium magnetic field to be in the y-direction, and
we derive the dispersion relation for small-amplitude instabilities and waves
in the large-|k_x| limit. We use the Routh-Hurwitz criterion to show
analytically that the necessary and sufficient criterion for stability in this
limit is n k_B dT/dz + dp_cr/dz + (1/8pi)dB^2/dz > 0, where T is the
temperature, n is the number density of thermal particles, and p_cr is the
cosmic-ray pressure. We present approximate analytical solutions for the normal
modes in the low- and high-diffusivity limits, show that they are consistent
with the derived stability criterion, and compare them to numerical results
obtained from the full, unapproximated, dispersion relation. Our results extend
earlier analyses of buoyancy instabilities in galaxy-cluster plasmas to the
beta <= 1 regime. Our results also extend earlier analyses of the Parker
instability to account for anisotropic thermal conduction, and show that the
interstellar medium is more unstable to the Parker instability than was
predicted by previous studies in which the thermal plasma was treated as
adiabatic.Comment: 36 pages, 2 figures, Accepted for publication in Ap
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