Time-Resolved Single-Particle X-ray Scattering Reveals Electron-Density Gradients As Coherent Plasmonic-Nanoparticle-Oscillation Source

Dynamics of optically excited plasmonic nanoparticles are presently understood as a series of scattering events involving the initiation of nanoparticle breathing oscillations. According to established models, these are caused by statistical heat transfer from thermalized electrons to the lattice. An additional contribution by hot-electron pressure accounts for phase mismatches between theory and experimental observations. However, direct experimental studies resolving the breathing-oscillation excitation are still missing. We used optical transient-absorption spectroscopy and time-resolved single-particle X-ray diffractive imaging to access the electron system and lattice. The time-resolved single-particle imaging data provided structural information directly on the onset of the breathing oscillation and confirmed the need for an additional excitation mechanism for thermal expansion. We developed a new model that reproduces all of our experimental observations. We identified optically induced electron density gradients as the initial driving source.

Cochlear sparing in LINAC-based radiosurgery for vestibular schwannoma: a dosimetric comparison of dynamic conformal arc, IMRT and VMAT treatment plans

BACKGROUND

Stereotactic radiosurgery (SRS) is the preferred treatment for vestibular schwannoma (VS) in patients with preserved hearing and tumour diameter < 3 cm. Emerging evidence suggests restricting cochlear dose could preserve hearing. This retrospective replanning study aims to compare dynamic conformal arc therapy (DCAT), intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) plans for superiority of cochlear dose sparing without compromising tumour coverage.

METHODS

Eligibility criteria included sporadic VS, serviceable hearing and availability of CT and MRI for planning. The original gross tumour volume and brainstem OAR volume were retained; the cochlea was newly contoured on the planning CT scan (bone window). Each case was replanned using the three above techniques, prescribing 12 Gy to the 80% isodose line. No dose constraint was applied to the cochlea.

RESULTS

Eighteen patients were replanned. Mean tumour volume was 2.25 cc. Tumour coverage and tumour mean dose (DCAT: 14.2, IMRT: 14.6, VMAT: 14.5 Gy) were comparable. Paddick and RTOG conformity indices were better for DCAT (0.66 and 1.6) and VMAT (0.69 and 1.5) compared to IMRT (0.56 and 1.9). DCAT had superior gradient index (3.0) compared to VMAT (3.4) and IMRT (3.4). VMAT delivered the lowest mean brainstem maximum dose (8.3 Gy) and decreased the mean cochlear dose (3.4 Gy) by 2.3 and 2.1 Gy, and the mean cochlear maximum dose (3.6 Gy) by 2.4 and 2.5 Gy relative to DCAT and IMRT, respectively.

CONCLUSION

LINAC-based SRS treatment using VMAT can achieve better cochlear dose sparing than DCAT or IMRT while maintaining tumour coverage.

The kinetic energy of PAH dication and trication dissociation determined by recoil-frame covariance map imaging

We investigated the dissociation of dications and trications of three polycyclic aromatic hydrocarbons (PAHs), fluorene, phenanthrene, and pyrene. PAHs are a family of molecules ubiquitous in space and involved in much of the chemistry of the interstellar medium. In our experiments, ions are formed by interaction with 30.3 nm extreme ultraviolet (XUV) photons, and their velocity map images are recorded using a PImMS2 multi-mass imaging sensor. Application of recoil-frame covariance analysis allows the total kinetic energy release (TKER) associated with multiple fragmentation channels to be determined to high precision, ranging 1.94-2.60 eV and 2.95-5.29 eV for the dications and trications, respectively. Experimental measurements are supported by Born-Oppenheimer molecular dynamics (BOMD) simulations.

Time-resolved relaxation and fragmentation of polycyclic aromatic hydrocarbons investigated in the ultrafast XUV-IR regime

Polycyclic aromatic hydrocarbons (PAHs) play an important role in interstellar chemistry and are subject to high energy photons that can induce excitation, ionization, and fragmentation. Previous studies have demonstrated electronic relaxation of parent PAH monocations over 10-100 femtoseconds as a result of beyond-Born-Oppenheimer coupling between the electronic and nuclear dynamics. Here, we investigate three PAH molecules: fluorene, phenanthrene, and pyrene, using ultrafast XUV and IR laser pulses. Simultaneous measurements of the ion yields, ion momenta, and electron momenta as a function of laser pulse delay allow a detailed insight into the various molecular processes. We report relaxation times for the electronically excited PAH^*, PAH^+* and PAH^2+* states, and show the time-dependent conversion between fragmentation pathways. Additionally, using recoil-frame covariance analysis between ion images, we demonstrate that the dissociation of the PAH²⁺ ions favors reaction pathways involving two-body breakup and/or loss of neutral fragments totaling an even number of carbon atoms.

XUV double-pulses with femtosecond to 650 ps separation from a multilayer-mirror-based split-and-delay unit at FLASH

Extreme ultraviolet (XUV) and X-ray free-electron lasers enable new scientific opportunities. Their ultra-intense coherent femtosecond pulses give unprecedented access to the structure of undepositable nanoscale objects and to transient states of highly excited matter. In order to probe the ultrafast complex light-induced dynamics on the relevant time scales, the multi-purpose end-station CAMP at the free-electron laser FLASH has been complemented by the novel multilayer-mirror-based split-and-delay unit DESC (DElay Stage for CAMP) for time-resolved experiments. XUV double-pulses with delays adjustable from zero femtoseconds up to 650 picoseconds are generated by reflecting under near-normal incidence, exceeding the time range accessible with existing XUV split-and-delay units. Procedures to establish temporal and spatial overlap of the two pulses in CAMP are presented, with emphasis on the optimization of the spatial overlap at long time-delays via time-dependent features, for example in ion spectra of atomic clusters.

CAMP@FLASH: an end-station for imaging, electron- and ion-spectroscopy, and pump-probe experiments at the FLASH free-electron laser

The non-monochromatic beamline BL1 at the FLASH free-electron laser facility at DESY was upgraded with new transport and focusing optics, and a new permanent end-station, CAMP, was installed. This multi-purpose instrument is optimized for electron- and ion-spectroscopy, imaging and pump-probe experiments at free-electron lasers. It can be equipped with various electron- and ion-spectrometers, along with large-area single-photon-counting pnCCD X-ray detectors, thus enabling a wide range of experiments from atomic, molecular, and cluster physics to material and energy science, chemistry and biology. Here, an overview of the layout, the beam transport and focusing capabilities, and the experimental possibilities of this new end-station are presented, as well as results from its commissioning.

A fast dual wavelength laser beam fluid-less optical CT scanner for radiotherapy 3D gel dosimetry I: design and development

Three dimensional dosimetry by optical CT readout of radiosensitive gels or solids has previously been indicated as a solution for measurement of radiotherapy 3D dose distributions. The clinical uptake of these dosimetry methods has been limited, partly due to impracticalities of the optical readout such as the expertise and labour required for refractive index fluid matching. In this work a fast laser beam optical CT scanner is described, featuring fluid-less and dual wavelength operation. A second laser with a different wavelength is used to provide an alternative reference scan to the commonly used pre-irradiation scan. Transmission data for both wavelengths is effectively acquired simultaneously, giving a single scan process. Together with the elimination of refractive index fluid matching issues, scanning practicality is substantially improved. Image quality and quantitative accuracy were assessed for both dual and single wavelength methods. The dual wavelength scan technique gave improvements in uniformity of reconstructed optical attenuation coefficients in the sample 3D volume. This was due to a reduction of artefacts caused by scan to scan changes. Optical attenuation measurement accuracy was similar for both dual and single wavelength modes of operation. These results established the basis for further work on dosimetric performance.

A fast dual wavelength laser beam fluid-less optical CT scanner for radiotherapy 3D gel dosimetry II: dosimetric performance

New clinical radiotherapy dosimetry systems need comprehensive demonstration of measurement quality. Practicality and reliability are other important aspects for clinical dosimeters. In this work the performance of an optical CT scanner for true 3D dosimetry is assessed using a radiochromic gel dosimeter. The fluid-less scanner utilised dual lasers to avoid the necessity for pre-irradiation scans and give greater robustness of image quality, enhancing practicality. Calibration methods using both cuvettes and reconstructed volumes were developed. Dosimetric accuracy was similar for dual and single wavelength measurements, except that cuvette calibration reliability was reduced for dual wavelength without pre-irradiation scanning. Detailed performance parameters were specified for the dosimetry system indicating the suitability for clinical use. The most significant limitations of the system were due to the gel dosimeter rather than the optical CT scanner. Quality assurance guidelines were developed to maintain dosimetry system performance in routine use.

[The Evaluation of the German Federal Law of Equal Treatment of Disabled Persons]

The German federal law of equal treatment of disabled persons (Behindertengleichstellungsgesetz des Bundes, BGG) came into effect in 2002. An evaluation of this law was required by the national plan of action for the implementation of the United Nations Convention on the Rights of Persons with Disabilities (CRPD). Project evaluation objectives were to estimate whether the needs of disabled persons were being met and whether the instruments proved to be adequate for fulfilling the aims of the law. Jurisprudential analyses in combination with surveys were used for this research. It was found that the BGG still lacks adequate publicity. Its impact, however, was assessed as positive. Results also indicate that there might be some shortcomings with regard to accessibility. For a closer examination, however, more data focusing on accessibility in the context of health care and rehabilitation is.

Method for the description of differences in the filamentous structure of the cytoskeleton in cultured cells

Over the last few years in vitro cell systems have been established for toxicological investigations. These systems permit the evaluation of effects on the basis of cultured cells in order to replace animal studies. Not only qualitative assessment of cytotoxic effects, but also efforts to quantify these intracellular changes have become more and more important to objectify the results which have been obtained. The cytoskeleton, a dynamic and sensitive system, seems to be a valuable morphological parameter to gain information about the intracellular alterations of drug-influenced cells. Depending on the dose of the substance administered, the cytoskeleton shows morphological alterations in specific components, which fulfill structural as well as metabolic regulatory functions and thus provide information on possible mechanisms. Normally, microtubules as well as the intermediate filament system from 3-dimensional networks. Treatment may induce contraction or depolymerization of the filamentous proteins. These alterations, seen in immunofluorescent preparations, can be quantified by means of a 2-dimensional Fourier transformation. As there is no statistical method to compare different spectra, the spatial frequency spectrum of the Fourier components has to be transformed to a 1-dimensional array. This step is performed by measuring the optical density of localised areas in the frequency spectrum. Using this transformation it is possible to compare the Fourier spectra belonging to different treatment groups.

Can charge recombination as caused by pH-dependent donor-side limitation in PS 2 account for high-energy-state quenching?

Schreiber and Neubauer (Photosynthesis Research 25: 279-293, 1990) have proposed a model which explains energy quenching by enhanced triplet formation as caused by charge recombination due to pH-dependent donor-side limitation. Quenching under these conditions is assumed to result from two mechanisms. Firstly, there is the withdrawal of excited states by charge recombination and formation of triplet states. Secondly, these triplet states can result in carotenoid triplets in the antenna which are supposed to quench excitons. Here, it is shown that quenching caused by both mechanisms can account for only about 25% of the experimentally observed energy quenching even under extremely favorable conditions. More likely, this number is less than 15%, as the contribution of the second step in the proposed triplet cycle is expected to be low as the life times of the carotenoid triplets are not long enough to cause the assumed quenching of excitons in the antenna.

Accidental and homicidal death in a psychiatric emergency room population

To identify potentially preventable mortality other than suicide among psychiatric emergency room patients, the authors compared the rates of accidental and homicidal death among 5,284 consecutive psychiatric emergency room patients with those expected for an age-, sex-, and race-matched sample of the general population. The rate of accidental death was two and one-half times and the rate of homicidal death nearly twice the expected rate for the matched general population. Diagnostic and demographic analyses indicated that increased risk of death from either cause was highest among alcoholics, schizophrenic patients, and males. The implications of the findings for clinical care are discussed.

Suicide in a psychiatric emergency room population

Twenty-two suicides were identified in a series of 5,284 psychiatric emergency room patients, yielding a suicide rate of 111.1 per 100,000 "patient-years at risk"--more than seven times the age- and sex-adjusted rate for the general population. Subpopulations at high risk were white people, men, depressed and schizophrenic patients, substance abusers, and patients with multiple emergency room visits. No patients had killed themselves immediately after an emergency room visit, but several had killed themselves without following through on a referral from the emergency room to another facility for treatment. The authors discuss the implications of these findings for emergency room practice and for further research.

Christmas and psychopathology. Data from a psychiatric emergency room population

It is widely believed among psychiatrists and laymen alike that Christmas and other holidays are associated with an increased incidence of psychopathology. Statistical studies, however, consistently have been shown the Christmas season to be associated with a low incidence of suicide and psychiatric hospitalization. The present study examines the number and type of visits to a 24-hour psychiatric emergency service over a seven-year period. There is a decrease in the number of visits during the days and weeks before Christmas and an increase of roughly the same magnitude afterward. The effect is more prominent for women and older persons but does not seem to differentially affect persons of different racial, marital, or diagnostic status.

Effects of alcohol on psychomotor performance of women: interaction with menstrual cycle

The effects of alcohol on performance were investigated in 10 ovulating young women. Placebo drink and three doses of alcohol were administered in a random order both during follicular and luteal phases of the menstrual cycle. The women had significantly slower verbal information processing rate and poorer visual detection performance during the follicular than the luteal phase of the menstrual cycle. In psychomotor tasks other than tracking, dose--response relationships of alcohol were different during the different phases of the menstrual cycle.

Effects of age and alcohol on psychomotor performance of men

Age and low doses of alcohol had a synergistic deleterious effect on subjects' performance on a continuous tracking task.

Stress and adaptation in later life

The effects of five major life events, and of three types of resources, on the physical and social-psychological adaptation of 375 participants in a longitudinal study were examined. As expected, medical events had the most impact on physical adaptation, but they had surprisingly little impact on social-psychological adaptation. Retirement had the most negative social-psychological effects, but had little effect on physical adaptation. The other three events had even less effects, although multiple events tended to cumulate in impact. Better physical resources helped only physical adaptation, and better psychological and social resources mainly helped satisfaction. It appears that most of these potential stressors have less serious long-term outcomes than the crisis orientation would suggest.

Treatment goals in geropsychiatry

Each geriatric patient has observable problems which can generate treatment goals implemented by a treatment plan. Extensive record keeping would be required to document this tripartite scheme. In practice, either problem-oriented or goal-oriented records are used. Problem records tend to drift toward a goal concept, since problems are usually stated in only sufficient detail to serve as a guide to treatment. The results of a problem-oriented format are described for 143 state hospital patients whose mean age was 74 years. The most common number of problems was 5 per patient. Physical problems were the most frequent (N equals 456), followed by behavioral (N equals 203), thought-related (N equals 156), administrative (N equals 99), affective (N equals 69), and attitudinal (N equals 10). The author's experience with both systems leaves them with preference for the problem-oriented system with geriatric patients since physical problems are so numerous.

Laser pumping by intense discharges in z-pinch geometry

Optical properties of high-current, low-pressure, noble-gas discharges in z-pinch geometry are studied and compared with theta-pinch discharges and standard commercial light sources. Results indicate possible usefulness in systems where high peak power, high repetition rates or high uv content are demanded.