Non-equilibrium lattice dynamics of one-dimensional In chains on Si(111) upon ultrafast optical excitation.

The photoinduced structural dynamics of the atomic wire system on the Si(111)-In surface has been studied by ultrafast electron diffraction in reflection geometry. Upon intense fs-laser excitation, this system can be driven in around 1 ps from the insulating [Formula: see text] reconstructed low temperature phase to a metastable metallic [Formula: see text] reconstructed high temperature phase. Subsequent to the structural transition, the surface heats up on a 6 times slower timescale as determined from a transient Debye-Waller analysis of the diffraction spots. From a comparison with the structural response of the high temperature [Formula: see text] phase, we conclude that electron-phonon coupling is responsible for the slow energy transfer from the excited electron system to the lattice. The significant difference in timescales is evidence that the photoinduced structural transition is non-thermally driven.

Optically excited structural transition in atomic wires on surfaces at the quantum limit.

Transient control over the atomic potential-energy landscapes of solids could lead to new states of matter and to quantum control of nuclear motion on the timescale of lattice vibrations. Recently developed ultrafast time-resolved diffraction techniques combine ultrafast temporal manipulation with atomic-scale spatial resolution and femtosecond temporal resolution. These advances have enabled investigations of photo-induced structural changes in bulk solids that often occur on timescales as short as a few hundred femtoseconds. In contrast, experiments at surfaces and on single atomic layers such as graphene report timescales of structural changes that are orders of magnitude longer. This raises the question of whether the structural response of low-dimensional materials to femtosecond laser excitation is, in general, limited. Here we show that a photo-induced transition from the low- to high-symmetry state of a charge density wave in atomic indium (In) wires supported by a silicon (Si) surface takes place within 350 femtoseconds. The optical excitation breaks and creates In-In bonds, leading to the non-thermal excitation of soft phonon modes, and drives the structural transition in the limit of critically damped nuclear motion through coupling of these soft phonon modes to a manifold of surface and interface phonons that arise from the symmetry breaking at the silicon surface. This finding demonstrates that carefully tuned electronic excitations can create non-equilibrium potential energy surfaces that drive structural dynamics at interfaces in the quantum limit (that is, in a regime in which the nuclear motion is directed and deterministic). This technique could potentially be used to tune the dynamic response of a solid to optical excitation, and has widespread potential application, for example in ultrafast detectors.

Ultra-fast electron diffraction at surfaces: from nanoscale heat transport to driven phase transitions.

Many fundamental processes of structural changes at surfaces occur on a pico- or femtosecond time scale. In order to study such ultra-fast processes, we have combined modern surface science techniques with fs-laser pulses in a pump-probe scheme. Reflection high energy electron diffraction (RHEED) with grazing incident electrons ensures surface sensitivity for the probing electron pulses. Utilizing the Debye-Waller effect, we studied the cooling of vibrational excitations in monolayer adsorbate systems or the nanoscale heat transport from an ultra-thin film through a hetero-interface on the lower ps-time scale. The relaxation dynamics of a driven phase transition far away from thermal equilibrium is demonstrated with the In-induced (8×2) reconstruction on Si(111). This surface exhibits a Peierls-like phase transition at 100K from a (8×2) ground state to (4×1) excited state. Upon excitation by a fs-laser pulse, this structural phase transition is driven into an excited (4×1) state at a sample temperature of 20K. Relaxation into the (8×2) ground state occurs after more than 150 ps.

A pulsed electron gun for ultrafast electron diffraction at surfaces.

The construction of a pulsed electron gun for ultrafast reflection high-energy electron diffraction experiments at surfaces is reported. Special emphasis is placed on the characterization of the electron source: a photocathode, consisting of a 10 nm thin Au film deposited onto a sapphire substrate. Electron pulses are generated by the illumination of the film with ultraviolet laser pulses of femtosecond duration. The photoelectrons are emitted homogeneously across the photocathode with an energy distribution of 0.1 eV width. After leaving the Au film, the electrons are accelerated to kinetic energies of up to 15 keV. Focusing is accomplished by an electrostatic lens. The temporal resolution of the experiment is determined by the probing time of the electrons traveling across the surface which is about 30 ps. However, the duration of the electron pulses can be reduced to less than 6 ps.

Indium square root 7 x square root 3 on Si(111): a nearly free electron metal in two dimensions.

We present measurements of the Fermi surface and underlying band structure of a single layer of indium on Si(111) with square root 7 x square root 3 periodicity. Electrons from both indium valence electrons and silicon dangling bonds contribute to a nearly free, two-dimensional metal on a pseudo-4-fold lattice, which is almost completely decoupled at the Fermi level from the underlying hexagonal silicon lattice. The mean free path inferred from our data is quite long, suggesting the system might be a suitable model for studying the ground state of two-dimensional metals.

Home monitoring service improves mean arterial pressure in patients with essential hypertension. A randomized, controlled trial.

BACKGROUND: Technological advances in the distribution of information have opened new avenues for patient care. Few trials, however, have used telemedicine to improve blood pressure in patients with essential hypertension. OBJECTIVE: To determine the efficacy of a telecommunication service in reducing blood pressure. DESIGN: Randomized, controlled trial. SETTING: University-affiliated primary care outpatient clinics. PATIENTS: 121 adults with essential hypertension who were under evaluation for a change in antihypertensive therapy. INTERVENTION: A home service consisting of automatic transmission of blood pressure data over telephone lines, computerized conversion of the information into report forms, and weekly electronic transmission of the report forms to physicians and patients. MEASUREMENTS: 24-hour ambulatory blood pressure monitoring at baseline and exit. The primary end point was change in mean arterial pressure from baseline to exit. RESULTS: Mean arterial pressure decreased by 2.8 mm Hg in patients receiving the home service and increased by 1.3 mm Hg in patients receiving usual care (P = 0.013 for the difference). Mean diastolic blood pressure decreased by 2.0 mm Hg for home service but increased by 2.1 mm Hg for usual care (P = 0.012 for the difference). Mean systolic blood pressure decreased by 4.9 mm Hg for home service and 0.1 mm Hg for patients receiving usual care (P = 0.047 for the difference). Among African-American patients, mean arterial pressure decreased by 9.6 mm Hg in those receiving home service and increased by 5.25 mm Hg in those receiving usual care (P = 0.047). Part of the decrease in blood pressure for home service was due to more frequent changes in the type or dose of antihypertensive medications. CONCLUSION: This telecommunication service was efficacious in reducing the mean arterial pressure of patients with established essential hypertension.

Metastatic breast cancer diagnosed during a work-up for urinary incontinence: a case report.

Breast cancer is the most commonly diagnosed cancer among women in the USA and the second leading cause of cancer deaths in women. Breast cancer metastases to the bladder are unusual but have been reported occasionally in the literature. The majority of the reports describe bladder metastases presenting with symptomatology or occurring in the context of disseminated disease. We present the case of an 87-year-old woman with a history of breast cancer and negative routine work-up for metastatic disease. She was referred to the urogynecology division in our institution because of complaints of urinary incontinence and urinary urgency. A urethrocystoscopy revealed suspicious bladder mucosal lesions that were biopsied. The pathology findings, when compared to the original cancer specimens, were consistent with metastatic disease. This case suggests that in patients with a history of breast cancer, even subtle urinary symptoms should be thoroughly evaluated.

Water soluble vitamin requirements in home parenteral nutrition patients.

Ascorbic acid, thiamin, niacin, pyridoxine, and folic acid status was evaluated in eight physiologically stable home parenteral nutrition patients. Six of these subjects received these vitamins as a twice weekly bolus and were studied over a period of 6 days. All vitamin levels were normal except for blood thiamin which was low, 72 h after each bolus. Since transketolase levels remained normal, this fall in blood thiamin probably had no functional significance. The urine excretion pattern of niacin and pyridoxine indicated normal metabolism and retention of these vitamins. Two patients, who required only parenteral fluid and electrolytes to remain weight stable, received none of these vitamins parenterally, but also maintained adequate vitamin status. These results suggest that in long term home parenteral nutrition patients these five vitamins can safely be given twice weekly, rather than daily, and that short bowel patients who maintain their weight without intravenous calories and protein also assimilate adequate amounts of these proximally absorbed water soluble vitamins from their diet.