High-speed THz spectroscopic imaging at ten kilohertz pixel rate with amplitude and phase contrast.

By combining the advantages of the high-speed ASOPS technology and efficient THz generation, we have realized a high-speed laser-based spectroscopic THz imaging system with more than 10,000 pixels per second acquisition speed and an excellent signal-to-noise ratio of more than 100. Unlike THz line cameras or mm-wave intensity detectors, the present device allows for a much higher spatial resolution and attributes each imaging pixel with phase and amplitude information up to several THz while simultaneously maintaining a very high scanning speed unmatched by any other technique presented so far. The high-speed acquisition allows for samples to be scanned even at sample velocities of 5 m/s or higher while preserving the fundamental resolution limit of the THz radiation, which is on the order of 500 µm in the present case.

Subharmonic resonant optical excitation of confined acoustic modes in a free-standing semiconductor membrane at GHz frequencies with a high-repetition-rate femtosecond laser.

We propose subharmonic resonant optical excitation with femtosecond lasers as a new method for the characterization of phononic and nanomechanical systems in the gigahertz to terahertz frequency range. This method is applied for the investigation of confined acoustic modes in a free-standing semiconductor membrane. By tuning the repetition rate of a femtosecond laser through a subharmonic of a mechanical resonance we amplify the mechanical amplitude, directly measure the linewidth with megahertz resolution, infer the lifetime of the coherently excited vibrational states, accurately determine the system's quality factor, and determine the amplitude of the mechanical motion with femtometer resolution.

Impulsive terahertz radiation with high electric fields from an amplifier-driven large-area photoconductive antenna.

We report on the generation of impulsive terahertz (THz) radiation with 36 kV/cm vacuum electric field (1.5 mW average thermal power) at 250 kHz repetition rate and a high NIR-to-THz conversion efficiency of 2 x 10(-3). This is achieved by photoexciting biased large-area photoconductive emitter with NIR fs pulses of microJ pulse energy. We demonstrate focussing of the THz beam by tailoring the pulse front of the exciting laser beam without any focussing element for the THz beam. A high dynamic range of 10(4) signal-to-noise is obtained with an amplifier based system.

Terahertz emission from lateral photo-Dember currents.

The photo-Dember effect is a source of impulsive THz emission following femtosecond pulsed optical excitation. This emission results from the ultrafast spatial separation of electron-hole pairs in strong carrier gradients due to their different diffusion coefficients. The associated time dependent polarization is oriented perpendicular to the excited surface which is inaptly for efficient out coupling of THz radiation. We propose a scheme for generating strong carrier gradients parallel to the excited surface. The resulting photo-Dember currents are oriented in the same direction and emit THz radiation into the favorable direction perpendicular to the surface. This effect is demonstrated for GaAs and In(0.53)Ga(0.47)As. Surprisingly the photo-Dember THz emitters provide higher bandwidth than photoconductive emitters. Multiplexing of phase coherent photo-Dember currents by periodically tailoring the photoexcited spatial carrier distribution gives rise to a strongly enhanced THz emission, which reaches electric field amplitudes comparable to a high-efficiency externally biased photoconductive emitter.

High-speed asynchronous optical sampling with sub-50fs time resolution.

We report an ultrafast time-domain spectroscopy system based on high-speed asynchronous optical sampling operating without mechanical scanner. The system uses two 1 GHz femtosecond oscillators that are offset-stabilized using high-bandwidth feedback electronics operating at the tenth repetition rate harmonics. Definition of the offset frequency, i.e. the time-delay scan rate, in the range of a few kilohertz is accomplished using direct-digital-synthesis electronics for the first time. The time-resolution of the system over the full available 1 ns time-delay window is determined by the laser pulse duration and is 45 fs. This represents a three-fold improvement compared to previous approaches where timing jitter was the limiting factor. Two showcase experiments are presented to verify the high time-resolution and sensitivity of the system.

Rapid-scanning terahertz precision spectrometer with more than 6 THz spectral coverage.

We report a terahertz time-domain spectrometer with more than 6 THz spectral coverage and 1 GHz resolution based on high-speed asynchronous optical sampling. It operates at 2 kHz scan rate without mechanical delay stage. The frequency error of the system at 60 s acquisition time is determined by comparing a measured water vapor absorption spectrum to data reported in the HITRAN database. The mean error of 87 evaluated absorption lines is 142 MHz.

The nature of the oxidation states of gold on ZnO.

The interaction between gold in the 0, i, ii and iii oxidation states and the zinc-terminated ZnO(0001) surface is studied via the QM/MM electronic embedding method using density functional theory. The surface sites considered are the vacant zinc interstitial surface site (VZISS) and the bulk-terminated island site (BTIS). We find that on the VZISS, only Au(0) and Au(i) are stable oxidation states. However, all clusters of i to iii oxidation states are stable as substitutionals for Zn2+ in the bulk terminated island site. Au(OH)(x) complexes (x= 1-3) can adsorb exothermically onto the VZISS, indicating that higher oxidation states of gold can be stabilised at this site in the presence of hydroxyl groups. CO is used as a probe molecule to study the reactivity of Au in different oxidation states in VZISS and BTIS. In all cases, we find that the strongest binding of CO is to surface Au(i). Furthermore, CO binding onto Au(0) is stronger when the gold atom is adsorbed onto the VZISS compared to CO binding onto a gas phase neutral gold atom. These results indicate that the nature of the oxidation states of Au on ZnO(0001) will depend on the type of adsorption site. The role of ZnO in Au/ZnO catalysts is not, therefore, merely to disperse gold atoms/particles, but to also modify their electronic properties.

Modeling platinum group metal complexes in aqueous solution.

We construct force fields suited for the study of three platinum group metals (PGM) as chloranions in aqueous solution from quantum chemical computations and report experimental data. Density functional theory (DFT) using the local density approximation (LDA), as well as extended basis sets that incorporate relativistic corrections for the transition metal atoms, has been used to obtain equilibrium geometries, harmonic vibrational frequencies, and atomic charges for the complexes. We found that DFT calculations of [PtCl(6)](2-).3H(2)O, [PdCl(4)](2-).2H(2)O, and [RhCl(6)](3-).3H(2)O water clusters compared well with molecular mechanics (MM) calculations using the specific force field developed here. The force field performed equally well in condensed phase simulations. A 500 ps molecular dynamics (MD) simulation of [PtCl(6)](2-) in water was used to study the structure of the solvation shell around the anion. The resulting data were compared to an experimental radial distribution function derived from X-ray diffraction experiments. We found the calculated pair correlation functions (PCF) for hexachloroplatinate to be in good agreement with experiment and were able to use the simulation results to identify and resolve two water-anion peaks in the experimental spectrum.

Sepsis from sinusitis in nasotracheally intubated patients. A diagnostic dilemma.

The cause of sepsis in the intensive care unit patient can be a perplexing diagnostic problem. We have recently encountered seven patients who had sepsis associated with sinusitis of the paranasal sinuses. They represented 26 percent of all patients who had nasotracheal intubation for 5 days or more. Sinusitis as a complication of nasotracheal intubation has been previously reported, but its frequency has not been appreciated. Three case reports are presented to emphasize the importance of making this diagnosis. Standard x-ray studies will not adequately demonstrate all the paranasal sinuses. We have utilized computerized tomography to study these patients and found it to clearly demonstrate all the paranasal sinuses. We suggest a plan to help prevent sinusitis from nasotracheal intubation. Should this complication occur, however, the nasotracheal tube should be removed and the sinuses surgically drained or treated aggressively with topical agents.

Role of subtotal colectomy in the treatment of incapacitating constipation.

Nine patients from a community surgical practice have been presented who underwent subtotal colectomy with ileal lower sigmoid anastomosis for the treatment of chronic incapacitating idiopathic constipation. Emphasis was placed on carefully selecting patients for this procedure. The results in this small series have been promising. Long-term follow-up is necessary to determine whether the patients will continue to do well. A review of the literature regarding the surgical treatment of constipation has indicated that subtotal colectomy is the most successful form of treatment in select patients. More studies are needed, specifically in the area of radiopaque markers and anorectal manometry, to determine whether or to what extent these procedures can help select patients who might benefit from this procedure.

Subtotal colectomy with primary anastomosis without diversion in the treatment of obstructing carcinoma of the left colon.

A small series of patients with obstruction from an adenocarcinoma of the left colon is presented. The recommended treatment in selected cases is subtotal colectomy with primary anastomosis without diversion. The morbidity and mortality in this small series was minimal compared with those reported in a much larger series of similar cases treated by bowel decompression with or without concomitant resection of the lesion. Further follow-up of this series is needed. However, this procedure should be considered seriously in selected patients with obstructing carcinoma of the left colon.

[Lysine biosynthesis of Pseudomonas aeruginosa PAO1. III. Further characterization of lysine auxotrophic mutant of Ps. aeruginosa PAO1]. / Lysinbiosynthese bei Pseudomonas aeruginosa PAO1. III. Weitere Charakterisierung Lysin-auxotropher Mutanten von Ps. Aeruginosa PAO1.

A number of lysine-auxotrophic mutants of Pseudomonas aeruginosa PAO1 were isolated through mutagenesis by means of N-methyl-N-nitrosoguaniine (Mach et al., unpublished). Using the cross feeding test and growth tests classification of lysine mutants was not possible. The investigation of diaminopimelic acid decarboxylase (DAP-DC) showed, that none of these mutants had an active enzyme, except for the mutants with a high number of revertants. The appearance of only one mutant type is attributed to the insufficient availability of DAP.