Asymmetric-cut variable-incident-angle monochromator.

A novel asymmetric-cut variable-incident-angle monochromator was constructed and tested in 1997 at the Advanced Photon Source of Argonne National Laboratory. The monochromator was originally designed as a high heat load monochromator capable of handling 5-10 kW beams from a wiggler source. This was accomplished by spreading the x-ray beam out on the surface an asymmetric-cut crystal and by using liquid metal cooling of the first crystal. The monochromator turned out to be a highly versatile monochromator that could perform many different types of experiments. The monochromator consisted of two 18° asymmetrically cut Si crystals that could be rotated about 3 independent axes. The first stage (Φ) rotates the crystal around an axis perpendicular to the diffraction plane. This rotation changes the angle of the incident beam with the surface of the crystal without changing the Bragg angle. The second rotation (Ψ) is perpendicular to the first and is used to control the shape of the beam footprint on the crystal. The third rotation (Θ) controls the Bragg angle. Besides the high heat load application, the use of asymmetrically cut crystals allows one to increase or decrease the acceptance angle for crystal diffraction of a monochromatic x-ray beam and allows one to increase or decrease the wavelength bandwidth of the diffraction of a continuum source like a bending-magnet beam or a normal x-ray-tube source. When the monochromator is used in the doubly expanding mode, it is possible to expand the vertical size of the double-diffracted beam by a factor of 10-15. When this was combined with a bending magnet source, it was possible to generate an 8 keV area beam, 16 mm wide by 26 mm high with a uniform intensity and parallel to 1.2 arc sec that could be applied in imaging experiments.

Clocking femtosecond X rays.

Linear-accelerator-based sources will revolutionize ultrafast x-ray science due to their unprecedented brightness and short pulse duration. However, time-resolved studies at the resolution of the x-ray pulse duration are hampered by the inability to precisely synchronize an external laser to the accelerator. At the Sub-Picosecond Pulse Source at the Stanford Linear-Accelerator Center we solved this problem by measuring the arrival time of each high energy electron bunch with electro-optic sampling. This measurement indirectly determined the arrival time of each x-ray pulse relative to an external pump laser pulse with a time resolution of better than 60 fs rms.

Distortion product otoacoustic emission and auditory brainstem responses in the echidna (Tachyglossus aculeatus).

The auditory function of four wild-caught echidnas was measured using distortion product otoacoustic emissions (DPOAEs) and auditory brainstem responses (ABRs). Emission audiograms were constructed by finding the stimulus levels required to produce a criterion emission amplitude at a given stimulus frequency. For an emission amplitude of -10 dB SPL, the median "best threshold" was 28 dB SPL, and this minimum threshold occurred between 4 and 8 kHz for all animals. The relative effective range of auditory function was defined by the frequencies at which the audiogram was 30 dB above its best threshold. For the emission audiograms, the median lower-frequency limit was 2.3 kHz, the upper limit was 18.4 kHz, and the effective range was 2.7 octaves. The audiogram as measured by ABR was also found to be strongly "U" shaped with similar low- and high-frequency limits, i.e., from 1.6 to 13.9 kHz, with an effective range of 3.1 octaves. These results suggest that the echidna has a behavioral hearing sensitivity comparable to that of typical therian mammals (e.g., rabbits and gerbils) but with a significantly narrower frequency range. DPOAE responses were also measured in selected animals as a function of the variation of all four stimulus parameters (frequencies and intensities of both stimulus tones). Overall, the measured emission responses establish that the echidna does have a cochlear amplifier, and that it could be the same type as in therian mammals. The amplification mechanism in the echidna, currently unidentified, clearly operates to frequencies above 20 kHz, higher than the hearing function observed in any birds or reptiles but lower than for typical therian mammals. This raises the possibility that at least some aspects of the mammalian cochlear amplifier developed early in evolution, before the divergence of the monotremes (echidna and platypus) from the mainstream therian mammals (marsupials and placentals). In this respect, the presence or absence of outer hair cell electromotility in monotremes would have important consequences for understanding the function and evolution of the vertebrate inner ear.

Air pollution and respiratory symptoms: results from three panel studies in Bangkok, Thailand.

Several studies in North American cities have reported associations between air pollution and respiratory symptoms. Replicating these studies in cities with very different population and weather characteristics is a useful way of addressing uncertainties and strengthening inferences of causality. To this end we examined the responses of three different panels to particulate matter (PM) air pollution in Bangkok, Thailand, a tropical city characterized by a very warm and humid climate. Panels of schoolchildren, nurses, and adults were asked to report daily upper and lower respiratory symptoms for 3 months. Concentrations of daily PM(10) (PM with a mass median aerodynamic diameter less than 10 microm) and PM(2.5) (airborne particles with aerodynamic diameters less than 2.5 microm) were collected at two sites. Generally, associations were found between these pollution metrics and the daily occurrence of both upper and lower respiratory symptoms in each of the panels. For example, an interquartile increase of 45 microg/m(3) in PM(10) was associated with about a 50% increase in lower respiratory symptoms in the panel of highly exposed adults, about 30% in the children, and about 15% in the nurses. These estimates were not appreciably altered by changes in the specification of weather variables, stratification by temperature, or inclusion of individual characteristics in the models; however, time trends in the data cause some uncertainty about the magnitude of the effect of PM on respiratory symptoms. These pollutants were also associated with the first day of a symptom episode in both adult panels but not in children. The estimated odds ratios are generally consistent with and slightly higher than the findings of previous studies conducted in the United States.

Two functional O-polysaccharide polymerase wzy (rfc) genes are present in the rfb gene cluster of Group E1 Salmonella enterica serovar Anatum.

Defined regions of the rfb gene cluster of Group E1 Salmonella enterica serovar Anatum were introduced into a mutated derivative of this strain that lacks O-polysaccharide polymerase activity. Three different kinds of assays performed on the various transformants all indicate that two functional wzy (rfc) genes reside within the Group E1 Salmonella rfb gene cluster. The product of ORF9.6, positioned near the center of the rfb gene cluster, joins O-polysaccharide repeat units together by alpha-glycosidic linkages to produce antigen O10, the major serological determinant of Group E1 S. enterica. The product of ORF17.4, positioned at the downstream end of the rfb gene cluster, can join repeat units together by beta-glycosidic linkages to produce antigen O15, the major serological determinant of Group E2 S. enterica.

Frequency responses of two- and three-tone distortion product otoacoustic emissions in Mongolian gerbils.

The frequency responses of distortion product otoacoustic emission (DPOAEs) were investigated in adult Mongolian gerbils. The main goal was to investigate in this species the extent to which DPOAE measurements might be useful in estimating cochlear frequency-tuning characteristics. Specifically, this study investigated the parameter space for generation of DPOAEs to determine those regions, if any, where the emission responses gave "simple" frequency responses, i.e., responses similar in form to typical neural responses. At the same time, it was desired to determine in this species the existence, extent, and nature of the more complex three-tone emission frequency responses as observed in some other species [e.g., Martin et al., Hearing Res. 136, 105-123 (1999)]. In the present work, two-tone frequency response curves (f2/f1 ratio functions) were obtained by varying the lower frequency, f1, while holding the f2 frequency and both amplitudes (L1, L2) constant. Only for frequencies, f2, near 8 kHz did the response at the emission frequency, 2 f1-f2, form a simple, relatively broad peak. At all lower frequencies, the two-tone frequency response curve was typically complex and composed of multiple peaks. In comparison, three-tone frequency responses were constructed by fixing the primary stimulus pair (f1, f2) and varying a third tone widely in frequency (f3) and intensity (L3). Points in f3 and L3 which caused a criterion reduction in primary emission amplitude (at 2 f1-f2) were used to construct emission suppression tuning curves (STCs). Only for primary frequencies, f2, at 8 kHz and above were the emission STCs found to be simple, with shapes similar to neural frequency-tuning curves. At lower primary frequencies, particularly for relatively low primary frequency ratios (low f2/f1), three-tone responses were very complex. This complex response usually included a region of anomalous suppression in which very low suppression levels (L3) could result in significant decreases in the primary emission amplitude, often exceeding 12 dB. Regions of such anomalous suppression were typically observed under the following conditions: (1) for all f2 frequencies from 0.5 to 4 kHz; (2) for f3 frequencies between 1.4 and 8 kHz; (3) i.e., for f3 frequencies 1-3 octaves above the primary frequency, f2; (4) at L3 levels often 10 dB lower or more than the usual "best frequency" threshold, i.e., even lower than the relative minimum threshold found near the primary stimulus frequencies; (5) exhibiting sharp amplitude decreases often accompanied by emission phase shifts of about 180 deg; (6) present in both cubic emissions (2 f1-f2 and 2 f2-f1); (7) to be less extreme at larger primary stimulus frequency ratios (larger f2/f1); and (8) less extreme at larger intensity ratios (larger L1/L2). Because of the anomalous behavior at f2 frequencies below 8 kHz, "simple" emission STCs were typically only obtainable, if at all, near the extreme boundaries of the parameter space giving measurable emission amplitudes.

A new high-speed beam chopper for time-resolved X-ray studies.

A new high-speed X-ray beam chopper, which can be phase locked to the temporal structure of the Advanced Photon Source (APS) storage ring, has been developed and tested. The open window time of the chopper is 2450 ns, which corresponds to approximately 67% of the revolution time of the APS storage ring. By phase locking the rotation of the beam chopper to the storage-ring orbital frequency, any portion of the storage-ring fill pattern can be positioned within the beam-chopper transmission-time window.

Performance limits of direct cryogenically cooled silicon monochromators - experimental results at the APS.

The successful use of cryogenically cooled silicon monochromators at third-generation synchrotron facilities is well documented. At the Advanced Photon Source (APS) it has been shown that, at 100 mA operation with the standard APS undulator A, the cryogenically cooled silicon monochromator performs very well with minimal (<2 arcsec) or no observable thermal distortions. However, to date there has not been any systematic experimental study on the performance limits of this approach. This paper presents experimental results on the performance limits of these directly cooled crystals. The results show that if the beam is limited to the size of the radiation central cone then, at the APS, the crystal will still perform well at twice the present 100 mA single 2.4 m-long 3.3 cm-period undulator heat load. However, the performance would degrade rapidly if a much larger incident white-beam size is utilized.

The historical development of cryogenically cooled monochromators for third-generation synchrotron radiation sources.

In the period of the late-1980s, before the construction of multi-GeV third-generation storage rings with their intense insertion-device sources, the perceived number one problem for X-ray instrumentation was proper cooling of the first optical element in the beamline. This article, first given as an acceptance speech for the Compton Award ceremony at the Advanced Photon Source, presents a somewhat historical and anecdotal overview of how cryogenically cooled monochromator optics have been developed to provide a monochromator cooling solution adequate for today's power levels. A series of workshops and international collaborations were the key components for the progress and final success of this development.

Parametric down conversion of X-ray photons.

Parametric down conversion of X-ray photons in diamond crystals was detected in two experiments, both using the phase-matching scheme first employed in the X-ray regime by Eisenberger & McCall [Phys. Rev. Lett. (1971), 26, 684-688]. The conversion events were detected by a combination of time-correlation spectroscopy and energy discrimination, using Si drift-chamber detectors. The time-correlation spectra give a direct comparison of the conversion rate over the accidental coincidence rate. Mechanisms for possible detection of false events and ways to cross check against them are discussed in detail.

Total condylar knee arthroplasty. 16- to 21-year results.

This study presents long term results of arthroplasty with posterior cruciate retention using the Total Condylar Knee implant. From 1976 to 1982, 139 patients had 159 knee arthroplasties using Total Condylar Knee prostheses. Sixty-three patients (72 knees) were available for followup at a minimum of 16 years (range, 16-21 years). The average age of the patients at the time of surgery was 61 years. There were 21 men and 42 women. Patients with 68 knees had osteoarthrosis, three had rheumatoid arthritis and one had posttraumatic arthritis. There were five delayed complications. One patient (one knee) underwent revision surgery and two patients (two knees) declined revision surgery because they were considered to be high surgical risks, as determined by their internists. The average preoperative score was 40.3 points and improved to 88.4 points at followup. Eighty-seven percent of the patients had a score equal to or more than 85 points at last evaluation. Prosthesis survivorship at 20 years was 98.6% for patients who had revision surgery. No femoral components were revised for aseptic loosening. Retention of the posterior cruciate in Total Condylar Knee prosthesis produces results comparable with the results of the original Total Condylar Knee prosthesis with cruciate sacrifice.

Genomic-sequence comparison of two unrelated isolates of the human gastric pathogen Helicobacter pylori.

Helicobacter pylori, one of the most common bacterial pathogens of humans, colonizes the gastric mucosa, where it appears to persist throughout the host's life unless the patient is treated. Colonization induces chronic gastric inflammation which can progress to a variety of diseases, ranging in severity from superficial gastritis and peptic ulcer to gastric cancer and mucosal-associated lymphoma. Strain-specific genetic diversity has been proposed to be involved in the organism's ability to cause different diseases or even be beneficial to the infected host and to participate in the lifelong chronicity of infection. Here we compare the complete genomic sequences of two unrelated H. pylori isolates. This is, to our knowledge, the first such genomic comparison. H. pylori was believed to exhibit a large degree of genomic and allelic diversity, but we find that the overall genomic organization, gene order and predicted proteomes (sets of proteins encoded by the genomes) of the two strains are quite similar. Between 6 to 7% of the genes are specific to each strain, with almost half of these genes being clustered in a single hypervariable region.

Cochlear implant performance after reimplantation: a multicenter study.

OBJECTIVE: This study compares auditory performance between original and replacement cochlear implants. STUDY DESIGN AND SETTING: Data from 18 U.S. cochlear implant programs were obtained by retrospective chart review. Patients received and returned subjective questionnaires. PATIENTS: Twenty-eight adults with once-functioning Nucleus 22 cochlear implants that failed received replacement Nucleus 22 cochlear implants in the same ears. MAIN OUTCOME MEASURES: Objective measures included sentence (CID Everyday Sentences or Iowa Sentences) and monosyllabic word (NU-6 Words or CNC Words) speech discrimination scores. Patients also rated and compared performance using subjective scales. RESULTS: Thirty-seven percent of patients had significantly higher sentence or word scores with their replacement cochlear implants than with their original implants, 26% had no significant change, and 37% had significantly poorer scores. Subjectively, 57% of patients reported that the performance of their replacement device was better or the same and 43% reported that it was poorer. There was no correlation between performance with the replacement cochlear implant and cause of the original device failure, duration of original device use before failure, surgical complications with either implantation, changes in electrode insertion depths, or preoperative variables, such as age, etiology, or duration of deafness. CONCLUSIONS: Speech recognition ability with a replacement cochlear implant may significantly increase or decrease from that with the original implant. Experienced cochlear implant patients facing reimplantation must be counseled regarding the possibility of differences in sound quality and speech recognition performance with their replacement device.

The effects of critical incident stress debriefing (CISD) on emergency medical services personnel following the Los Angeles Civil Disturbance.

This study examined the effects of Critical Incident Stress Debriefing (CISD) upon technicians who provided emergency medical services in South Central Los Angeles during the 1992 Los Angeles Civil Disturbance. The relationships between exposure, debriefing and symptoms of stress were identified and examined. The Frederick Reaction Index-Adult (FRI-A) was used to measure the presence of symptoms characteristic of posttraumatic stress disorder. EMTs who had the opportunity to participate in Critical Incident Stress Debriefings (n = 42) following the incident reported fewer symptoms and scored significantly lower on the FRI-A than those not participating in Critical Incident Stress Debriefing (n = 23).

Multi-layered PZT/polymer composites to increase signal-to-noise ratio and resolution for medical ultrasound transducers.

Increasing transducer bandwidth and signal-to-noise ratio (SNR) is fundamental to improving the quality of medical ultrasound images. In previous work, the authors have proposed the use of multi-layer 1-3 PZT/epoxy composites to increase both but have encountered significant fabrication challenges. These difficulties include making the bond thickness between the layers extremely small relative to the ultrasound wavelength and aligning the posts of the composite to increase the coupling coefficient. The authors have routinely achieved a bond thickness of less than 5 mum but aligning the posts is more complicated. Finite element (PZFlex; Weidlinger, Assoc., New York, NY and Los Altos, CA) simulations show that the pulse-echo SNR and bandwidth degrade significantly with misalignment of the posts. Alignment of greater than 90% of the post pitch (i.e., tolerance of 10 to 20 mum) is required to obtain significant increases in SNR and bandwidth relative to conventional transducer arrays. This will be a difficult tolerance for large-scale production. Thus, the authors have developed a multi-layer composite hybrid array that will not require post alignment. This structure consists of a layer of 5 MHz 1-3 composite material on top of conventional 5 MHz PZT, which will provide greater SNR relative to conventional composites and increased bandwidth over multi-layer PZT. PZFlex simulations show that for a 2 MHz linear array element, the 2 layer hybrid structure increases the pulse-echo SNR by 7.5 dB over that from a single layer PZT element. Even without a matching layer, an increase in the -6 dB pulse-echo fractional bandwidth from 22% for the PZT element to 35% for the hybrid element was also predicted. Experimentally, in a 32 element array, the authors achieved an increase of 5.2 dB in SNR and an increased -6 dB bandwidth from 23 to 30%. In vitro and in vivo images showed corresponding improvements.

Development of the base of the cochlea: place code shift in the gerbil.

Distortion product otoacoustic emission measurements were made at 1/12 octave intervals before and after the injection of furosemide in gerbils aged 15 days after birth to adult, in order to obtain estimates of cochlear amplifier gain as a function of stimulus frequency. The frequency at which the gains went sharply to zero, defined as the 'base cutoff frequency', increased from about 20 kHz to over 50 kHz during development. This increase provides further confirmation of the hypothesis that the place code changes during development in the basal part of the cochlea. If the measured base cutoff frequency is identified with the characteristic frequency at the basal end of the cochlea, as defined by electrophysiological measures, then these emission data can be used to generate a frequency-place map as a function of age. The derived place code shift is consistent with published electrophysiological measures, and can be used to extend these measures. Near the base cutoff frequency, the observed cochlear amplifier gain typically dropped sharply from a relative maximum to zero, over a distance of about a half octave. Specifically, this distance appeared to exhibit a curvilinear variation with age, reaching a maximum of 3/4 of an octave at 19-21 days. After transforming from frequency to place using the map derived from emissions, however, the distance between the extreme base and the place associated with the peak gain decreased monotonically from about 1.2 mm at age 15-19 days to 0.6 mm at maturity. This distance is assumed to be characteristic of the length of the active amplification zone for the cochlear amplifier in the base region. Over the same time period, there was approximately a doubling of the rate of amplification with distance from the base, so that the cochlear amplifier gain at the peak actually changed very little from 15 days to adult.