A high-power, high-repetition-rate THz source for pump-probe experiments at Linac Coherent Light Source II

Experiments using a THz pump and an X-ray probe at an X-ray free-electron laser (XFEL) facility like the Linac Coherent Light Source II (LCLS II) require frequency-tunable (3 to 20 THz), narrow bandwidth (∼10%), carrier-envelope-phase-stable THz pulses that produce high fields (>1 MV cm^-1) at the repetition rate of the X-rays and are well synchronized with them. In this paper, a two-bunch scheme to generate THz radiation at LCLS II is studied: the first bunch produces THz radiation in an electromagnet wiggler immediately following the LCLS II undulator that produces X-rays from the second bunch. The initial time delay between the two bunches is optimized to compensate for the path difference in THz transport. The two-bunch beam dynamics, the THz wiggler and radiation are described, as well as the transport system bringing the THz pulses from the wiggler to the experimental hall.

Volt-per-Ångstrom terahertz fields from X-ray free-electron lasers

The electron linear accelerators driving modern X-ray free-electron lasers can emit intense, tunable, quasi-monochromatic terahertz (THz) transients with peak electric fields of V Å-1 and peak magnetic fields in excess of 10 T when a purpose-built, compact, superconducting THz undulator is implemented. New research avenues such as X-ray movies of THz-driven mode-selective chemistry come into reach by making dual use of the ultra-short GeV electron bunches, possible by a rather minor extension of the infrastructure.

A Dataset for Three-Dimensional Distribution of 39 Elements Including Plant Nutrients and Other Metals and Metalloids in the Soils of a Forested Headwater Catchment

Quantification and evaluation of elemental distribution in forested ecosystems are key requirements to understand element fluxes and their relationship with hydrological and biogeochemical processes in the system. However, datasets supporting such a study on the catchment scale are still limited. Here we provide a dataset comprising spatially highly resolved distributions of 39 elements in soil profiles of a small forested headwater catchment in western Germany () to gain a holistic picture of the state and fluxes of elements in the catchment. The elements include both plant nutrients and other metals and metalloids that were predominately derived from lithospheric or anthropogenic inputs, thereby allowing us to not only capture the nutrient status of the catchment but to also estimate the functional development of the ecosystem. Soil samples were collected at high lateral resolution (≤60 m), and element concentrations were determined vertically for four soil horizons (L/Of, Oh, A, B). From this, a three-dimensional view of the distribution of these elements could be established with high spatial resolution on the catchment scale in a temperate natural forested ecosystem. The dataset can be combined with other datasets and studies of the TERENO (Terrestrial Environmental Observatories) Data Discovery Portal () to reveal elemental fluxes, establish relations between elements and other soil properties, and/or as input for modeling elemental cycling in temperate forested ecosystems.

Probing ultra-fast processes with high dynamic range at 4th-generation light sources: Arrival time and intensity binning at unprecedented repetition rates

Understanding dynamics on ultrafast timescales enables unique and new insights into important processes in the materials and life sciences. In this respect, the fundamental pump-probe approach based on ultra-short photon pulses aims at the creation of stroboscopic movies. Performing such experiments at one of the many recently established accelerator-based 4th-generation light sources such as free-electron lasers or superradiant THz sources allows an enormous widening of the accessible parameter space for the excitation and/or probing light pulses. Compared to table-top devices, critical issues of this type of experiment are fluctuations of the timing between the accelerator and external laser systems and intensity instabilities of the accelerator-based photon sources. Existing solutions have so far been only demonstrated at low repetition rates and/or achieved a limited dynamic range in comparison to table-top experiments, while the 4th generation of accelerator-based light sources is based on superconducting radio-frequency technology, which enables operation at MHz or even GHz repetition rates. In this article, we present the successful demonstration of ultra-fast accelerator-laser pump-probe experiments performed at an unprecedentedly high repetition rate in the few-hundred-kHz regime and with a currently achievable optimal time resolution of 13 fs (rms). Our scheme, based on the pulse-resolved detection of multiple beam parameters relevant for the experiment, allows us to achieve an excellent sensitivity in real-world ultra-fast experiments, as demonstrated for the example of THz-field-driven coherent spin precession.

Below gap optical absorption in GaAs driven by intense, single-cycle coherent transition radiation

Single-cycle terahertz fields generated by coherent transition radiation from a relativistic electron beam are used to study the high field optical response of single crystal GaAs. Large amplitude changes in the sub-band-gap optical absorption are induced and probed dynamically by measuring the absorption of a broad-band optical beam generated by transition radiation from the same electron bunch, providing an absolutely synchronized pump and probe geometry. This modification of the optical properties is consistent with strong-field-induced electroabsorption. These processes are pertinent to a wide range of nonlinear terahertz-driven light-matter interactions anticipated at accelerator-based sources.

Decompression illness in goats following simulated submarine escape: 1993-2006

The United Kingdom Ministry of Defence commissioned work to define the relationship between the internal pressure of a distressed submarine (DISSUB), the depth from which escape is made and the risk of decompression illness (DCI). The program of work used an animal model (goat) to define these risks and this paper reports the incidence and type of DCI observed. A total of 748 pressure exposures comprising saturation only, escape only or saturation followed by escape were conducted in the submarine escape simulator between 1993 and 2006. The DCI following saturation exposures was predominantly limb pain, whereas following escape exposures the DCI predominantly involved the central nervous system and was fast in onset. There was no strong relationship between the risk of DCI and the range of escape depths investigated. The risk of DCI incurred from escape following saturation was greater than that obtained by combining the risks for the independent saturation only, and escape only, exposures. The output from this program of work has led to improved advice on the safety of submarine escape.

Beam loading by distributed injection of electrons in a plasma wakefield accelerator

We show through experiments and supporting simulations that propagation of a highly relativistic and dense electron bunch through a plasma can lead to distributed injection of electrons, which depletes the accelerating field, i.e., beam loads the wake. The source of the injected electrons is ionization of the second electron of rubidium (Rb II) within the wake. This injection of excess charge is large enough to severely beam load the wake, and thereby reduce the transformer ratio T. The reduction of the average T with increasing beam loading is quantified for the first time by measuring the ratio of peak energy gain and loss of electrons while changing the beam emittance. Simulations show that beam loading by Rb II electrons contributes to the reduction of the peak accelerating field from its weakly loaded value of 43  GV/m to a strongly loaded value of 26  GV/m.

Coherent-radiation spectroscopy of few-femtosecond electron bunches using a middle-infrared prism spectrometer

Modern, high-brightness electron beams such as those from plasma wakefield accelerators and free-electron laser linacs continue the drive to ever-shorter bunch durations. In low-charge operation (~20 pC), bunches shorter than 10 fs are reported at the Linac Coherent Light Source (LCLS). Though suffering from a loss of phase information, spectral diagnostics remain appealing as compact, low-cost bunch duration monitors suitable for deployment in beam dynamics studies and operations instrumentation. Progress in middle-infrared (MIR) imaging has led to the development of a single-shot, MIR prism spectrometer to characterize the corresponding LCLS coherent beam radiation power spectrum for few-femtosecond scale bunch length monitoring. In this Letter, we report on the spectrometer installation as well as the temporal reconstruction of 3 to 60 fs-long LCLS electron bunch profiles using single-shot coherent transition radiation spectra.

Genetic background influences the behavioural and molecular consequences of neurokinin-1 receptor knockout

Genetic background affects animal phenotype and therefore is of particular relevance to studies using genetically manipulated mice. Strain differences in hypothalamic-pituitary-adrenocortical (HPA) axis activity may contribute to background-specificity of some mutations. Here, we analysed components of the HPA axis in mice lacking a functional neurokinin-1 receptor (NK1-/-) on two backgrounds: backcrossed C57BL/6 (B6) and mixed C57BL/6 x 129/sv (129B6). We hypothesized that HPA axis activity would vary between these strains, leading to differences in the NK1-/- phenotype. We compared levels of plasma corticosterone between the groups, and found 129B6 mice exhibited elevated levels of stress-induced corticosterone compared with B6 mice, regardless of genotype. Although the level of basal corticotrophin-releasing factor and stress-induced c-fos mRNAs did not differ between the genotypes of either strain, examination of glucocorticoid receptor immunoreactivity within the hippocampus revealed that NK1-/- mice on the 129B6 background had elevated expression compared with wild-type, whilst there was no difference between genotypes in the B6 strain. Similarly, hippocampal neurogenesis in NK1-/- mice was greater than in wild-type on the 129B6 strain, and did not differ between genotypes on the B6 background. Finally, novelty- and morphine-induced locomotion were assessed. NK1-/- mice on the 129B6 background exhibited hyperlocomotion in response to novelty and greater sensitivity to the locomotor-stimulating properties of morphine than wild-type. In contrast, in B6 mice, no differences were observed between genotypes for either locomotor behaviour. In summary, we find that HPA axis activity differs between the strains and that there are profoundly background-specific effects of the NK1 receptor mutation.

Evaluation of bluetongue virus diagnostic tests in free-ranging bighorn sheep

Five bluetongue virus (BTV) diagnostic tests were evaluated for use in free-ranging bighorn sheep. We sampled one bighorn sheep population four times between 1989 and 1995. The tests evaluated included virus isolation (VI), polymerase-chain reaction (PCR), serum neutralization (SN), agar-gel immunodiffusion (AGID), and competitive enzyme-linked immunosorbent assay (c-ELISA). The c-ELISA, AGID and SN tests had high levels of agreement in determining serogroup exposure in bighorn sheep. We used maximum-likelihood algorithms to estimate the parameters of each diagnostic test used. Although the c-ELISA and AGID had high sensitivity and specificity, the SN had perfect specificity but lower apparent sensitivity. Due to the potential of cross-reactions among multiple serotypes, results of the SN must be interpreted with caution when assessing serotype exposure in an area where multiple serotypes are endemic. The PCR assay delineated convalescent antibody titers from more-recent infections, and consequently, was pivotal in distinguishing a different exposure pattern between the bighorn sheep and cattle in an adjacent herd. Based on an increasing seroprevalence (50% to 100%), BTV circulated through this bighorn sheep population between 1989 and 1993. This increase in seroprevalence coincided with a bighorn die-off due to BTV infection in June, 1991. An adjacent cattle herd was sampled in 1995 for comparison. The bighorn sheep and adjacent cattle had different patterns of exposure to BTV between 1994 and 1995. There was no evidence that BTV circulated through the bighorn sheep population from 1994 to 1995. In 1995, seroprevalence to BTV decreased to 72%, none of yearling bighorn was seropositive, and all of the 39 bighorn sheep were PCR-negative. In contrast, all adult cattle were seropositive to BTV by c-ELISA and SN, and 4 of the calves were seropositive; 11 of the 24 cattle were PCR-positive, including all five calves. Overall, the pattern of temporal herd immunity in the bighorn sheep appeared to follow a classic epidemic curve, with the appearance and subsequent disappearance of herd immunity coinciding with the 1991 die-off in this population. As low levels of herd immunity and high proportions of susceptible animals are key factors in the development of epidemics, this population of bighorn sheep may be at increased risk for a BTV epidemic in the future.

Isolation of three classes of conditional lethal Chinese hamster ovary cell mutants with temperature-dependent defects in low density lipoprotein receptor stability and intracellular membrane transport

Fluorescence-activated cell sorting was used to isolate 19 independent, temperature-sensitive, low density lipoprotein (LDL) receptor-deficient Chinese hamster ovary cell mutants that define three recessive complementation groups, ldlE, ldlF, ldlG. LDL receptor activity, essentially normal at the permissive temperature (34 degrees C), was virtually abolished in the mutants after incubation for 8-12 h at the nonpermissive temperature (39-40.5 degrees C). The mutants died after incubation for > 24 h at 39.5 degrees C. These mutants exhibited two striking and unexpected abnormalities that suggest that they define three genes important for general vesicular membrane traffic. First, LDL receptors were degraded abnormally rapidly at the nonpermissive temperature (chloroquine inhibited this degradation in ldlE and ldlG, but not in ldlF). In ldlE cells, the rapid degradation did not require efficient receptor clustering into coated pits and was not observed for all cell surface proteins. This selective degradation may be due to endocytic missorting. Second, the mutants exhibited temperature-sensitive defects in the posttranslational processing and intracellular transport of many membrane-associated and secreted proteins, including the LDL, mannose 6-phosphate/insulin-like growth factor II, and scavenger receptors, the vesicular stomatitis virus G protein and decay accelerating factor. Although the initial synthesis, folding, and processing of precursor forms of these proteins in the endoplasmic reticulum were apparently normal at the nonpermissive temperature, there was either a delay or a block in oligosaccharide processing associated with endoplasmic reticulum to medial Golgi transport at the nonpermissive temperature. This was accompanied by a dramatic inhibition of total soluble protein secretion. The posttranslational processing defects, the instability of cell surface LDL receptors, and the defective protein secretion exhibited by these mutants suggest that the ldlE-G gene products regulate or participate in reactions that are vital for a variety of secretory and endocytic membrane transport processes. This suggestion is strongly supported by our recent observation that a cDNA encoding a component of the coatomer, epsilon-COP, corrects the mutant phenotypes of ldlF cells (Guo, Q., Vasile, E., and Krieger, M. (1994) J. Cell Biol. 125, 1213-1224). Thus, these mutant cells should prove useful for further genetic and biochemical analysis of the mechanisms underlying intracellular membrane traffic.

Strain differences in consumption of saline solutions by mice

Intake of saline (NaCl) solutions and water by males of two inbred strains of mice [C57BL/6J (C57) and 129/J] were examined using 48-h, two-bottle preference tests. There was a large strain difference in saline intake: at moderate concentrations (0.075-0.150 M) C57 mice tended to reject saline relative to water, whereas 129/J mice preferred it. Both strains of mice increased their intake of saline following lasix-induced sodium depletion and the preference exhibited by 129/J mice for 0.15 M NaCl was eliminated following LiCl toxicosis. The rejection of moderate concentrations of saline by C57 was shown to be due, in part at least, to prior exposure to iso- or hypertonic saline solutions: C57 mice that had no prior exposure to saline exhibited a greater intake of saline than C57 mice previously exposed to 0.30 M NaCl. Saline preferences of the 129/J mice were not affected by prior exposure to 0.30 M NaCl. Thus, the strain difference in mouse salt preference is due in part to postingestional consequences of saline consumption in C57 but not 129/J mice.

The interstitial fluid pressure monitor: a device to aid in the determination of patient fluid requirements

Assessment of patient fluid requirements is often difficult. Previous basic as well as clinical studies have suggested that interstitial fluid pressure (IFP) correlates with interstitial fluid volume and can be measured with a catheter placed in the subcutaneous space. We constructed a simple device to monitor IFP. The mean IFP for 7 healthy volunteers was -1.19 mmHg. IFP was measured in 25 patients at presentation and as clinical status evolved. Patients were classified as hypervolemic, normovolemic, or hypovolemic on the basis of their clinical status, the evolution of their condition, and laboratory and radiographic data. IFP correlation with assigned classification was statistically significant. The results suggest IFP can be measured readily and reliably in humans and is sensitive for reflecting the hydration of the interstitial compartment. This measure can assist in the determination of patient fluid requirements.