Laser-writable high-k dielectric for van der Waals nanoelectronics

Similar to silicon-based semiconductor devices, van der Waals heterostructures require integration with high-k oxides. Here, we demonstrate a method to embed and pattern a multifunctional few-nanometer-thick high-k oxide within various van der Waals devices without degrading the properties of the neighboring two-dimensional materials. This transformation allows for the creation of several fundamental nanoelectronic and optoelectronic devices, including flexible Schottky barrier field-effect transistors, dual-gated graphene transistors, and vertical light-emitting/detecting tunneling transistors. Furthermore, upon dielectric breakdown, electrically conductive filaments are formed. This filamentation process can be used to electrically contact encapsulated conductive materials. Careful control of the filamentation process also allows for reversible switching memories. This nondestructive embedding of a high-k oxide within complex van der Waals heterostructures could play an important role in future flexible multifunctional van der Waals devices.

New routes to the functionalization patterning and manufacture of graphene-based materials for biomedical applications

Graphene-based materials are being widely explored for a range of biomedical applications, from targeted drug delivery to biosensing, bioimaging and use for antibacterial treatments, to name but a few. In many such applications, it is not graphene itself that is used as the active agent, but one of its chemically functionalized forms. The type of chemical species used for functionalization will play a key role in determining the utility of any graphene-based device in any particular biomedical application, because this determines to a large part its physical, chemical, electrical and optical interactions. However, other factors will also be important in determining the eventual uptake of graphene-based biomedical technologies, in particular the ease and cost of manufacture of proposed device and system designs. In this work, we describe three novel routes for the chemical functionalization of graphene using oxygen, iron chloride and fluorine. We also introduce novel in situ methods for controlling and patterning such functionalization on the micro- and nanoscales. Our approaches are readily transferable to large-scale manufacturing, potentially paving the way for the eventual cost-effective production of functionalized graphene-based materials, devices and systems for a range of important biomedical applications.

Changes in Skin Microcirculation at Periulcerous Sites in Patients with Chronic Venous Ulcers during Leg Elevation

Objective:

To investigate the effect of limb elevation on the microcirculation of the skin in patients with venous ulceration of the leg.

Design:

Prospective study in patients receiving in patient treatment for venous ulceration.

Setting:

Health Service teaching hospital.

Patients:

Thirteen patients with venous ulceration of the lower limb for more than two years were investigated.

Interventions:

Patients were admitted to hospital and treated by bedrest with elevation of the lower limbs by 10° above the horizontal.

Main outcome measures:

Laser Doppler fluximetry and transcutaneous oximetry of the skin surrounding the venous ulcers was undertaken.

Results:

The laser Doppler fluximetry in the periculcerous region increased by 10.8 A.U. (95% CI 17 to 4.54). However, the transcutaneous oxygen measurements did not change during the period of treatment.

Conclusions:

Admission to hospital with elevation of the limb for patients with venous ulceration results in ***microcirculatory changes which are probably attributable to reduction in lower limb oedema.

How to Measure Changes in Oedema in Patients with Chronic Venous Ulcers?

objective:

To assess changes in limb volume and oedema in Patients admitted to hospital for treatment of venous ulceration.

Design:

Prospective study in thirteen patients.

Setting:

Health Service teaching hospital.

Patients:

Thirteen patients with venous ulceration for 2 years.

Interventions:

Patients were admitted to hospital for bed-rest and lower limb elevation for a period of 24 hours

Main outcome measures:

Limb volume was measured by water displacement and impedance plethysmography.

Results:

During limb elevation there was a mean reduction limb volume of 524 mls (95% CI 377–671 mls) after 24 hours of bedrest. This corresponded with a reduction in impedance measured by the impedance plethysmograph of 19–0 ohms (95% CI 24.3 to 15.6 ohms).

Conclusion:

Measurement of the lower limb volume by water displacement and by impedance plethysmography are likely to be useful methods in the investigation of Patients with chronic venous insufficiency.

Spectroscopy of discrete vertically oriented single-crystals of n-type tetraazaterrylene: understanding the role of defects in molecular semiconductor photovoltaics

Oriented single crystals of tetra-aza-terrylene (TAT), and photoluminescence of pristine and defect structures.

Properties and applications of chemically functionalized graphene

The vast and yet largely unexplored family of graphene materials has great potential for future electronic devices with novel functionalities. The ability to engineer the electrical and optical properties in graphene by chemically functionalizing it with a molecule or adatom is widening considerably the potential applications targeted by graphene. Indeed, functionalized graphene has been found to be the best known transparent conductor or a wide gap semiconductor. At the same time, understanding the mechanisms driving the functionalization of graphene with hydrogen is proving to be of fundamental interest for energy storage devices. Here we discuss recent advances on the properties and applications of chemically functionalized graphene.

Properties and applications of chemically functionalized graphene

The vast and yet largely unexplored family of graphene materials has great potential for future electronic devices with novel functionalities. The ability to engineer the electrical and optical properties in graphene by chemically functionalizing it with a molecule or adatom is widening considerably the potential applications targeted by graphene. Indeed, functionalized graphene has been found to be the best known transparent conductor or a wide gap semiconductor. At the same time, understanding the mechanisms driving the functionalization of graphene with hydrogen is proving to be of fundamental interest for energy storage devices. Here we discuss recent advances on the properties and applications of chemically functionalized graphene.

Polarization-driven stark shifts in quantum dot luminescence from single CdSe/oligo-PPV nanoparticles

We demonstrate polarization-induced spectral shifts and associated linearly polarized absorption and emission in single CdSe/oligo-(phenylene vinylene) (CdSe/OPV) nanoparticles. A mechanism for these observations is presented in which charge separation from photoexcited ligands results in a significant Stark distortion of the quantum dot electron/hole wavefunctions. This distortion results in an induced linear polarization and an associated red shift in band-edge photoluminescence. These studies suggest the use of single quantum dots as local charge mobility probes.

Linear dipole behavior in single CdSe-oligo(phenylene vinylene) nanostructures

We report on linearly polarized absorption and emission from individual (4.3 nm) CdSe quantum dots whose surfaces are coordinated with monodisperse oligo-phenylene vinylene ligands. Shown previously to suppress quantum dot blinking, we demonstrate here that the electronic interaction of photoexcited ligands with the quantum dot core is manifested as a strong polarization anisotropy in absorption (M = 0.5), as well as distinct linear dipole emission patterns from the quantum dot core. Further, there is a correlation between the quantum dot emission moment and polarization orientation corresponding to the absorption maxima that is manifested as fluctuations in emission moment orientation in the X-Y plane. The observed polarization effects can be switched off by tuning the excitation away from the ligand absorption band. We propose a mechanism based on exciton dissociation from the photoexcited ligand, followed by the pinning of electrons at the quantum dot surface. The resulting Stark interaction is sufficiently strong to break the 2D degeneracy of the emission moment within the dot, and may therefore account for the linear dipole emission character.

Blinking suppression and intensity recurrences in single CdSe-oligo(phenylene vinylene) nanostructures: experiment and kinetic model

We report time-resolved single molecule fluorescence imaging of individual CdSe quantum dots that are functionalized with oligomeric conjugated organic ligands. The fluorescence intensity trajectories from these composite nanostructures display both a strong degree of blinking suppression and intensity fluctuations with characteristic recurrence times on the order of 10-60 s. In addition, fluorescence decay rate measurements of individual hybrid nanostructures indicate significantly modified non-radiative quantum dot decay rates relative to conventional ZnS-capped CdSe quantum dots. We show that a modified diffusive reaction coordinate model with slow fluctuations in quantum dot electron energies (1S(e), 1P(e)) can reproduce the experimentally observed behaviour.

Fluorescence lifetimes and correlated photon statistics from single CdSe/oligo(phenylene vinylene) composite nanostructures

We present measurements of fluorescence intensity trajectories and associated excited-state decay times from individual CdSe/oligo(phenylene vinylene) (CdSe-OPV) quantum dot nanostructures using time-tagged, time-resolved (TTTR) photon counting techniques. We find that fluorescence decay times for the quantum dot emitter in these composite systems are at least an order of magnitude shorter than ZnS-capped CdSe quantum dot systems. We show that both the blinking suppression and associated lifetime/count rate behavior can be described by a modified version of the diffusive reaction coordinate model which couples slow fluctuations in quantum dot electron (1Se, 1Pe) energies to Auger-assisted hole trapping processes, hence modifying both blinking statistics and excited-state decay rates.

Photonic polymers:a new class of photonic wire structure from intersecting polymer-blend microspheres

We report a new kind of photonic wire structure made from the sequential attachment of polymer-blend microparticles. Using a linear quadrupole to manipulate the particles in space, we are able to take advantage of a modified surface structure in the blend particle to actively assemble particles in programmable two- or three-dimensional architectures. Strong resonance features in fluorescence are observed near the intersection of linked spheres that cannot be interpreted with a two-dimensional (equatorial plane) model. Three-dimensional ray optics calculations show long-lived periodic trajectories that propagate in great circles linked at an angle with respect to the plane containing the sphere centers.

Three-dimensional photonic "molecules" from sequentially attached polymer-blend microparticles

We report the observation of 3D linear or branched chains of polymer-blend microspheres generated from liquid droplets of solution where the modified surface structure of the polymer composite results in highly robust interparticle bonds. Using a linear quadrupole to precisely position particles in space, we are able to take advantage of this novel material property to actively assemble particles in programmable three-dimensional architectures. The robust interlocking nature of interparticle linkage gives rise to strongly coupled morphology-dependent resonances in bisphere and trisphere systems, suggesting the possibility of three-dimensional photonic "molecules" and microscale optical manipulation applications.

Health-related variables and academic performance among first-year college students: implications for sleep and other behaviors

The authors analyzed the effect of several health behaviors and health-related variables on grade point averages of a random sample of 200 students living in on-campus residence halls at a large private university. The set of variables included exercise, eating, and sleep habits; mood states; perceived stress; time management; social support; spiritual or religious habits; number of hours worked per week; gender; and age. Of all the variables considered, sleep habits, particularly wake-up times, accounted for the largest amount of variance in grade point averages. Later wake-up times were associated with lower average grades. Variables associated with the 1st-year students' higher grade point averages were strength training and study of spiritually oriented material. The number of paid or volunteer hours worked per week was associated with lower average grades.

Spindle cell angiosarcoma of the oropharynx

Angiosarcomas are uncommon malignant tumours of vascular endothelium. In the head and neck, the scalp is the commonest site of origin. A rare case of spindle-cell angiosarcoma of the oropharynx, treated by surgery and post-operative radiotherapy, is reported. We discuss the clinical presentation and histopathological diagnosis of this lesion.

Fluorescence imaging of single molecules in polymer microspheres

We report on far-field fluorescence imaging of single molecules in spherical polymer microparticles produced from solution by using microdroplet techniques. The fluorescence photobleaching quantum yields of rhodamine 6G in a common water-soluble polymer (polyvinyl alcohol) are at least five times smaller, corresponding to proportionally larger average fluorescence signals, than those in ethanolic solvents. This allows for acquisition of multiple images from a single molecule on a time scale of several minutes. We also show that fluorescent images of single molecules in microspheres can be calculated from semiclassic electrodynamics, which may ultimately be useful in retrieving dynamical information from experimental images.

Single-molecule analysis of ultradilute solutions with guided streams of 1--microm water droplets

We describe instrumentation for real-time detection of single-molecule fluorescence in guided streams of 1-microm (nominal) water droplets. In this technique, target molecules were confined to droplets whose volumes were comparable with illumination volumes in diffraction-limited fluorescence microscopy and guided to the waist of a cw probe laser with an electrostatic potential. Concentration detection limits for Rhodamine 6G in water were determined to be approximately 1 fM, roughly 3 orders of magnitude lower than corresponding limits determined recently with diffraction-limited microscopy techniques for a chemical separation of similar dyes. In addition to its utility as a vehicle for probing single molecules, instrumentation for producing and focusing stable streams of 1-2-microm-diameter droplets may have other important analytical applications as well.

The relationship of economic factors and stress among employed, married women with children

A convenience sample of 62 married women with children at home were measured on five economic variables and three stress-related variables: mother/marital role satisfaction, mother work role fulfillment and physical indicators of stress. The analysis reveals several significant relationships for the fulfillment and stress variables. Regression analysis also was used to model the relationship among economic and stress-related variables. The study suggests that financial health modules be integrated into stress management and other health enhancement programs for married, employed women.

Homogeneous polymer blend microparticles with a tunable refractive index

We show that homogeneous polymer blend microparticles can be prepared in situ from droplets of dilute solution of codissolved polymers. Provided that the droplet of solution is small enough (<10 mum), solvent evaporation is rapid enough to inhibit phase separation. Thus the polymers that are being mixed need not be miscible, which greatly enhances the applicability of the technique. From analysis of two-dimensional Fraunhofer diffraction (angular scattering) patterns, we show that both the real and the imaginary parts of the refractive index can be tuned by adjustment of the relative weight fractions of polymers in solution.

Generalizability theory: a unified approach to assessing the dependability (reliability) of measurements in the health sciences

The reliability of health promotion program evaluation measures, behavioral and attitudinal measures, and clinical measures is a concern to many health educators. Classical reliability coefficients, such as Cronbach's alpha, apply to narrowly defined, prespecified measurement situations. Classical theory does not provide adequate reliability assessments for criterion-referenced measures, for measurement situations having multiple sources of error, or for aggregate-level variables. Generalizability theory can be used to assess the reliability of measures in these situations that are not adequately modeled by Classical theory. Additionally, Generalizability theory affords a broader view and a deeper understanding of the dependability of measurements and the role of different sources of error in the variability of measures.

Time-domain observation of optical pulse propagation in whispering-gallery modes of glass spheres

We report picosecond time-resolved measurements of optical pulse propagation in dielectric spheres (8, 10, and 26 mm in diameter) for which the pulse duration ( approximately 2 ps) was short compared with the equatorial round-trip time within the sphere. A size-independent buildup of the leakage intensity in terms of the number of round trips was observed for each of the spheres, as were damped low-frequency oscillations superimposed upon the pulse ringdown envelope. These features of the data are interpreted as resulting from perturbative coupling of eigenmodes of the sphere and trajectory precession near the observation region.

Spatial photoselection of single molecules on the surface of spherical microcavities

We show that ultrasensitive microdroplet-stream fluorescence techniques combined with surfactant forms of Rhodamine dyes can be used to probe single molecules on the surfaces of spherical microcavities. Individual octadecyl Rhodamine B molecules, shown previously by ensemble measurements to be localized and oriented at the surfaces of liquid microspheres, were spatially photoselected primarily along great circles lying perpendicular or parallel to the detection axis by use of polarized laser excitation. A polarization dependence is observed in the distribution of single-molecule fluorescence amplitudes that can be interpreted qualitatively in terms of position-dependent fluorescence-collection efficiencies.

Real-time observation of single-molecule fluorescence in microdroplet streams

We report real-time observation of fluorescence bursts from individual Rhodamine 6G molecules in streams of microdroplets (peak signal-to-noise ratios, approximately 30) whose trajectories are constrained with a linear electric quadrupole. This approach offers a reasonable dynamic range in droplet size (3- 12-microm diameter) with <1% shot-to-shot size fluctuations and sensitivity comparable with that of droplet levitation techniques with at least 10(3) higher analysis rates. Applications to the study of single-molecule microcavity effects and stimulated emission are discussed.

Collection of fluorescence from single molecules in microspheres: effects of illumination geometry

The collection of fluorescence from a molecule inside a sphere illuminated with single or counterpropagating plane waves is modeled. The results are applicable to microdroplet-based single molecule detection techniques and to some microparticle characterization techniques using inelastic emission. The large position-dependent variations in the fluorescence collection rate are primarily attributable to variations in the excitation intensity. With plane-wave illumination the collection from shadow regions is low because the incident energy is refracted by the droplet surface away from these regions. The average collection rate from molecules in shadow regions can be increased by illuminating with counterpropagating beams.

Modeling fluorescence collection from single molecules in microspheres: effects of position, orientation, and frequency

We present calculations of fluorescence from single molecules (modeled as damped oscillating dipoles) inside a dielectric sphere. For an excited molecule at an arbitrary position within the sphere we calculate the fluorescence intensity collected by an objective in some well-defined detection geometry. We find that, for the cases we model, integration over the emission linewidth of the molecule is essential for obtaining representative results. Effects such as dipole position and orientation, numerical aperture of the collection objective, sphere size, emission wavelength, and linewidth are examined. These results are applicable to single-molecule detection techniques employing microdroplets.

Using storyboarding to determine components of wellness for university students

Using a needs-assessment technique called storyboarding to determine characteristics of health promotion and wellness among university students is discussed. Storyboarding allows students to work together as they generate ideas and eliminates the territorial defensiveness that often occurs when new ideas are suggested. Sixteen graduate students in a health education teaching methods course demonstrated the use of the technique to identify characteristics of wellness for university students. In addition, they identified content areas and outlined key programs, services, personal habits, and skills useful for enhancing university students' wellness.

Probing Chemical Reactions: Evidence for Exploration of an Excited Potential Energy Surface at Thermal Energies

The reaction K + NaBr --> KBr + Na is probed during the reactive collision by a continuous wave laser tuned to frequencies not resonant with excitation in either reagents or products. Transient [K..Br..Na] absorbs a laser photon giving [K..Br..Na](*), which can decompose to Na(*) + KBr. Emission from excited Na(*) at the sodium D lines provides direct evidence of laser absorption during the reaction. Different excitation spectra were observed, depending on which sodium D line was monitored. This difference is explicable if, in the absence of the laser, the reaction flux partially bifurcates to a second potential energy surface during the reaction.

Effectiveness of antibiotic prophylaxis in preventing bacteriuria after multichannel urodynamic investigations: a blind, randomized study in 124 female patients

One hundred twenty-four women with chronic, persistent lower urinary tract symptoms who had been scheduled for elective urodynamic investigations at Mount Sinai's Urodynamic Investigative Unit were divided into two blind, randomized groups, receiving either a placebo or prophylactic antibiotic. At the time of urodynamic testing, the rate of unsuspected urinary tract infection was 8.1%. There was no statistically significant decrease in postinstrumentation infection rate in the group who received prophylactic antibiotics. We conclude that, given in the fashion described in the study, prophylactic antibiotics are not effective in preventing urinary tract infections caused by urodynamic testing.

Glimpses into measurements of the microcirculation in skin

There are instances when chronic disease states manifest as microvascular disturbances of the skin. Objective assessment of these disturbances would permit a better understanding of the causative factors and, in certain circumstances, influence decisions of clinical management. Recent advances in technology that permit such assessment non-invasively are evaluated in this review.

Birth dates of trigeminal motoneurons and metamorphic reorganization of the jaw myoneural system in frogs

Drastic alterations in oral behavior characterize metamorphosis of anuran amphibians. Changes cascade through all components of the jaw apparatus from bone to muscle to nerve. In this investigation, tritiated thymidine autoradiography was used to determine the production schedule of the trigeminal motoneurons in the leopard frog, Rana pipiens. The time of origin of these neurons and their subsequent fate are of special interest given the breakdown of the larval jaw muscles and the de novo generation of adult muscle fibers during metamorphosis. Specifically, we wanted to learn whether trigeminal motoneurons are added, deleted, or reused during metamorphic climax. The entire complement of trigeminal motoneurons was produced over a 4-day span commencing at embryonic stage 13 and terminating at stage 20. Newly formed neurons are added to the primordial trigeminal nucleus in an orderly pattern. Firstborn neurons settle in the ventrorostral region of the nucleus; cells with progressively later birth dates were added in a posterodorsal direction. No additional trigeminal motoneurons are generated during larval maturation or at metamorphosis, thus indicating that the same population of neurons is present throughout the lifespan of the animal. From these observations we suggest that, during metamorphosis, the trigeminal motoneurons that supply the larval muscles switch their allegiance to the newly formed adult jaw muscles. This change of peripheral targets can be viewed as a respecification of the trigeminal motoneurons.

Maturation and recycling of trigeminal motoneurons in anuran larvae

Development of the trigeminal motor system was analyzed in Rana pipiens larvae and adults. The aim of this investigation was to determine the postmetamorphic fate of the primary motoneurons that innervate the larval jaw muscles. Specifically, we wanted to ascertain whether these neurons were deleted in conjunction with their muscular targets during metamorphosis or reused to innervate the adult jaw muscles. Cell counts and horseradish peroxidase tracer were used to distinguish between these two possibilities. The number of trigeminal motoneurons was relatively constant in premetamorphic and prometamorphic larvae. A small reduction in the cellular complement of the motor nucleus occurred during metamorphic climax, but the majority (approximately equal to 90%) of the primary motoneurons were retained from the larval to the adult nervous system. The cell loss may represent motoneurons that innervated specific larval muscles that have no adult successors and thus the entire myoneural unit degenerates. Retrograde tracers indicated that all trigeminal motoneurons extended axons into the jaw muscles of both premetamorphic larvae and adult frogs. These observations provide further support for the recycling of the trigeminal motoneurons.