bluuebunny/crossref_metadata_2025 huggingface dataset:
Poroelastic rebound along the Landers 1992 earthquake surface rupture
Authors: Peltzer Gilles , Rosen Paul , Rogez Francois , Hudnut K.
Published: February 2004

Maps of surface displacement following the 1992 Landers, California, earthquake, generated by interferometric processing of ERS‐1 synthetic aperture radar (SAR) images, reveal effects of various postseismic deformation processes along the 1992 surface rupture. The large‐scale pattern of the postseismic displacement field includes large lobes, mostly visible on the west side of the fault, comparable in shape with the lobes observed in the coseismic displacement field. This pattern and the steep displacement gradient observed near the Emerson‐Camp Rock fault cannot be simply explained by afterslip on deep sections of the 1992 rupture. Models show that horizontal slip occurring on a buried dislocation in a Poisson's material produces a characteristic quadripole pattern in the surface displacement field with several centimeters of vertical motion at distances of 10–20 km from the fault, yet this pattern is not observed in the postseismic interferograms. As previously proposed to explain local strain in the fault step overs [Peltzer et al., 1996b], we argue that poroelastic rebound caused by pore fluid flow may also occur over greater distances from the fault, compensating the vertical ground shift produced by fault afterslip. Such a rebound is explained by the gradual change of the crustal rocks' Poisson's ratio value from undrained (coseismic) to drained (postseismic) conditions as pore pressure gradients produced by the earthquake dissipate. Using the Poisson's ratio values of 0.27 and 0.31 for the drained and undrained crustal rocks, respectively, elastic dislocation models show that the combined contributions of afterslip on deep sections of the fault and poroelastic rebound can account for the range change observed in the SAR data and the horizontal displacement measured at Global Positioning System (GPS) sites along a 60‐km‐long transect across the Emerson fault [Savage and Svarc, 1997]. Using a detailed surface slip distribution on the Homestead Valley, Kickapoo, and Johnson Valley faults, we modeled the poroelastic rebound in the Homestead Valley pull apart. A Poisson's ratio value of 0.35 for the undrained gouge rocks in the fault zone is required to account for the observed surface uplift in the 3.5 years following the earthquake. This large value implies a seismic velocity ratio Vp/Vs of 2.1, consistent with the observed low Vs values of fault zone guided waves at shallow depth [Li et al., 1997]. The SAR data also reveal postseismic creep along shallow patches of the Eureka Peak and Burnt Mountain faults with a characteristic decay time of 0.8 years. Coseismic, dilatant hardening (locking process) followed by post‐seismic, pore pressure controlled fault creep provide a plausible mechanism to account for the decay time of the observed slip rate along this section of the fault.
Three‐dimensional upper crustal heterogeneity and anisotropy around Hole 504B from seismic tomography
Authors: Detrick Robert S. , Toomey Douglas R. , Collins John A.
Published: February 2004

We have used over 16,000 compressional wave travel times recorded on 11 ocean bottom seismometers to determine the magnitude of P‐wave heterogeneity and anisotropy in the upper 2 km of the oceanic crust in an ∼150 km2 area around Hole 504B, the deepest hole drilled into the oceanic crust. Our best fitting one‐dimensional, isotropic upper crustal velocity model for the 150 km2 area around the drill site is similar to velocity models at Hole 504B determined using downhole sonic logs, vertical seismic profiles, oblique seismic experiments and conventional refraction profiling. There is no evidence seismic layer 2 is anomalously thin at Hole 504B, suggesting that the occurrence of the seismic layer 2/3 boundary within the upper sheeted dike section, which has been documented in Hole 504B, is a general feature of this 5.9 Ma crust. On the scale of a few kilometers and averaged over seismic wavelengths of a few hundred meters the heterogeneity in upper crustal P wave velocity around Hole 504B is comparatively small. Within the 571‐m thick extrusive section maximum P wave velocity differences are ∼300–400 m s−1 (a 6%–8% velocity anomaly). These velocity differences decrease to <100–200 m s−1 (<2%–3% of the average velocity) within the sheeted dike section >1 km into the crust. The highest upper crustal velocities are found beneath basement ridges west and south of Hole 504B, while the lowest upper crustal velocities occur beneath the flanking basement troughs. There is an azimuthal dependence to the travel time residuals (slow direction N‐S) which is consistent with 2%–4% crack‐induced anisotropy in the upper crust. The magnitude of upper crustal heterogeneity observed near Hole 504B is significantly less than that found in “zero‐age” crust at the Mid‐Atlantic Ridge but comparable to that observed off‐axis in crust formed at faster spreading ridges.
Synthetic aperture radar interferometry coherence analysis over Katmai volcano group, Alaska
Authors: Lu Zhong , Freymueller Jeffrey T.
Published: February 2004

The feasibility of measuring volcanic deformation or monitoring deformation of active volcanoes using space‐borne synthetic aperture radar (SAR) interferometry depends on the ability to maintain phase coherence over appropriate time intervals. Using ERS 1 C band (λ=5.66 cm) SAR imagery, we studied the seasonal and temporal changes of the interferometric SAR coherence for fresh lava, weathered lava, tephra with weak water reworking, tephra with strong water reworking, and fluvial deposits representing the range of typical volcanic surface materials in the Katmai volcano group, Alaska. For interferograms based on two passes with 35 days separation taken during the same summer season, we found that coherence increases after early June, reaches a peak between the middle of July and the middle of September, and finally decreases until the middle of November when coherence is completely lost for all five sites. Fresh lava has the highest coherence, followed by either weathered lava or fluvial deposits. These surfaces maintain relatively high levels of coherence for periods up to the length of the summer season. Coherence degrades more rapidly with time for surfaces covered with tephra. For images taken in different summers, only the lavas maintained coherence well enough to provide useful interferometric images, but we found only a small reduction in coherence after the first year for surfaces with lava. Measurement of volcanic deformation is possible using summer images spaced a few years apart, as long as the surface is dominated by lavas. Our studies suggest that in order to make volcanic monitoring feasible along the Aleutian arc or other regions with similar climatic conditions, observation intervals of the satellite with C band SAR should be at least every month from July through September, every week during the late spring/early summer or late fall, and every 2–3 days during the winter.
Long submarine lava flows: Observations and results from numerical modeling
Authors: Gregg Tracy K. P. , Fornari Daniel J.
Published: February 2004

Long (>100 km) lava flows are relatively common on Mars and Venus and have been identified on the Moon, but they are rarely documented on Earth. However, although ∼75% of the Earth's surface is covered by water, only a small percentage of the ocean floor has been investigated at a resolution sufficient to unequivocally identify the boundaries of long submarine lava flows. Even so, basaltic lava flows as long as 110 km have been identified on the deep (>1500 m) seafloor near Hawaii and the East Pacific Rise. Ambient conditions on the deep ocean floor may favor the development of long lava flows for the following reasons. First, high pressures (>15 MPa) keep volatiles dissolved in basaltic lavas, preventing viscosity increases associated with exsolution and vesiculation. Second, seawater rapidly quenches the surface of submarine basalt flows so that an insulating glass layer, 1–5 cm thick, encases submarine flows within seconds after their emplacement. This glass rind effectively insulates the molten flow interior from additional heat loss, making submarine basalt flows behave as well‐insulated, subaerial tube‐fed flows. Thus, for identical basalt flows emplaced on the deep seafloor and subaerially, a submarine flow could advance farther before stopping. Results of numerical modeling indicate that thin (≤1 m) submarine basalt flows behave similarly to identical subaerial flows, but thicker submarine flows may advance significantly farther than their subaerial counterparts.
Phase equilibrium constraints on the viscosity of silicic magmas: 1. Volcanic‐plutonic comparison
Authors: Scaillet Bruno , Holtz François , Pichavant Michel
Published: February 2004

By using recently determined experimental phase equilibria we show that the viscosity of granitic magmas emplaced at upper crustal levels is approximately constant at ∼104.5 Pa s, irrespective of their temperature and level of emplacement. Magmas crystallizing as granitic plutons are not water‐poor and thus not more viscous than their extrusive equivalents. Instead, comparison between pre‐eruption magma viscosities of extrusive silicic‐intermediate and intrusive granitic magmas shows that the former are on average slightly more viscous. Given the typical strain rates in silicic magma chambers, magma rheological behavior is expected to be dominantly Newtonian, bubbles having a minor rheological influence at depth although exceptions can exist. Thus whether a silicic‐intermediate magma is erupted or frozen at depth depends primarily on the rheological properties of surrounding terranes or on external tectonic factors, but not on the rheology of the magma itself. However, preemptive viscosities of extrusive magmas rarely exceed 106 Pa.s, which suggests that crystal‐melt mushes with higher viscosities cannot leave the magma storage regions beneath volcanoes. The narrow range of viscosities displayed by silicic‐intermediate magmas results from both the strong control that pressure exerts on volatile solubilities in silicate melts and thermal limitations required to produce acid magmas. Considerations of the relationships between magma crystallinities, bulk SiO2, and preemptive melt H2O contents show that the higher the melt H2O content is the higher the maximum crystallinity that a given magma will be while still being potentially erupted. An empirical correlation is proposed that enables us to estimate preemptive melt H2O contents of erupted magmas by knowing their crystallinity and bulk SiO2.
Seismic structure of the southern Cascadia subduction zone and accretionary prism north of the Mendocino triple junction
Authors: Gulick Sean P. S. , Meltzer Anne M. , Clarke Samuel H.
Published: February 2004

Four multichannel‐seismic reflection profiles, collected as part of the Mendocino triple junction seismic experiment, image the toe of the southern Cascadia accretionary prism. Today, 250–600 m of sediment is subducting with the Gorda plate, and 1500–3200 m is accreting to the northern California margin. Faults imaged west and east of the deformation front show mixed structural vergence. A north‐south trending, 20 km long portion of the central margin is landward vergent for the outer 6–8 km of the toe of the prism. This region of landward vergence exhibits no frontal thrust, is unusually steep and narrow, and is likely caused by a seaward‐dipping backstop close to the deformation front. The lack of margin‐wide preferred seaward vergence and wedge‐taper analysis suggests the prism has low basal shear stress. The three southern lines image wedge‐shaped fragments of oceanic crust 1.1–7.3 km in width and 250–700 m thick near the deformation front. These wedges suggest shortening and thickening of the upper oceanic crust. Discontinuities in the seafloor west of the prism provide evidence for mass wasting in the form of slump blocks and debris fans. The southernmost profile extends 75 km west of the prism imaging numerous faults that offset both the Gorda basin oceanic crust and overlying sediments. These high‐angle faults, bounding basement highs, are interpreted as strike‐slip faults reactivating structures originally formed at the spreading ridge. Northeast or northwest trending strike‐slip faults within the basin are consistent with published focal mechanism solutions and are likely caused by north‐south Gorda‐Pacific plate convergence.
A new mechanism of slip weakening and strength recovery of friction associated with the mechanical consolidation of gouge
Authors: Nakatani Masao
Published: February 2004

I present results of a series of slide‐hold‐slide tests on granite surfaces separated by a layer of simulated granite gouge. The shear stress during the hold period (τhold) was controlled and used as a major control parameter of the experiments in addition to the time of hold. Time‐dependent fault healing, which has been observed in many previous similar experiments, was observed only at very high τhold, above 90% of the sliding friction. A time‐independent strengthening termed “consolidation strengthening” occurred at all τhold, with a magnitude proportional to the reduction of τhold. The magnitude of this strengthening was as large as 25% of the residual friction. The consolidation strengthening was found to be erased by subsequent slip in quite a different manner than is time‐dependent healing. The friction decreased linearly with slip displacement at a rate independent of the magnitude of the strengthening and hence larger slip displacement is required to erase larger consolidation strengthening. On the basis of these results together with earlier authors' results of the measurements of porosity change under similar conditions, I conclude that the time‐independent strengthening is due to the occurrence of gouge particle rearrangement to tighter packing enabled by decreased shear stress (under a constant normal stress) and that the subsequent slip weakening is due to unconsolidation of gouge enabled by particle rearrangement (dilatancy) during shearing. The rate‐ and state‐dependent friction (RSF) law was extended to incorporate the present findings.
Laboratory observations of fault‐normal vibrations during stick slip
Authors: Bodin Paul , Brown Stephen , Matheson Duncan
Published: February 2004

We report laboratory observations of interface separation waves during stick slip on a fault in a uniform polymer material. Our observations, made at stress levels expected at midcrustal depths, share many macroscopic properties with ruptures of faults in rocks. We observed a drop in fault‐normal stress shortly before the onset of, and during, stick slip at points along the fault during a rupture. We suggest that P wave energy in front of the propagating rupture tip is responsible for the drop in normal stress. We also interpret that stick slip took place within a traveling slip pulse, and we suggest that the dynamic stress drop within the slipping patch exceeded the overall static stress drop by a factor of at least 5 within a few millimeters of the fault. Our experiments did not resolve whether the fault surfaces actually separate or if fault‐normal stress is just greatly reduced. In either case the net result is that fault slip is permitted to take place with much less factional resistance than that expected from the applied load. Our observations provide laboratory evidence that fault‐normal vibrations may play an important role in sustaining a rupture by facilitating the propagation of a transient instability. Faults may appear weak in part because they are dynamically weakened as they slip during rupture while retaining their strength during the interseismic period.
Lithospheric anisotropy beneath the Pyrenees from shear wave splitting
Authors: Barruol Guilhem , Souriau Annie , Vauchez Alain , Diaz Jordi , Gallart Josep , Tubia José , Cuevas Julia
Published: February 2004

We investigate upper mantle anisotropy beneath the Pyrenean range along three N‐S profiles across the mountain belt. The results of a first profile that operated in 1993 in the central part of the belt have been presented elsewhere. We present the results of two other profiles that ran in 1995–1996 and 1996–1997 in the eastern and western part of the belt, respectively and propose an interpretation of the whole results. Teleseismic shear waves (SKS, SKKS, and PKS) are used to determine splitting parameters: the fast polarization direction ϕ and the delay time δt. Teleseismic shear wave splitting in the eastern Pyrenees displays homogeneous ϕ values trending N100°E and δt values in the range 1.1 to 1.5 s. A station located in the southern Massif Central, 100 km north of the range, is characterized by different splitting parameters (ϕ=N70°E, δt=0.7 s). In the western part of the belt, anisotropy parameters are similar across the whole belt (ϕ=N110°E and δt=1.3 to 1.5 s). Most of the measured delay times, including those obtained in the central part of the range, are above the global average of the SKS splitting (around 1 s). At the belt scale, ϕ is generally poorly correlated with recent estimations of the absolute plate motion, which predicts a fast direction ranging between N50°E and N80°E. Instead, the orientation of ϕ (N100°E) is parallel to the trend of the Pyrenean belt but also to Hercynian preexisting structures. This parallelism supports an anisotropy primarily related to frozen or active lithospheric structures. We show that a signature related to the Pyrenean orogeny is likely for the stations located in the internal domains of the belt. By contrast, the anisotropy measured at the stations located on the external parts of the belt could reflect a pre‐Pyrenean (Hercynian) deformation. We suggest that a late Hercynian strike‐slip deformation is responsible for this frozen upper mantle anisotropy and that the Pyrenean tectonic fabric developped parallel to this preexisting fabric. Finally, no particularly strong splitting is related to the North Pyrenean Fault, commonly believed to represent the plate boundary between Iberia and Eurasia.
The size distribution of pyroclasts and the fragmentation sequence in explosive volcanic eruptions
Authors: Kaminski E. , Jaupart C.
Published: February 2004

In an explosive eruption, the atmospheric column dynamics depend strongly on the mass fraction of gas in the erupting mixture, which is fixed by fragmentation in the volcanic conduit. At fragmentation, gas present in vesicular magmatic liquid gets partitioned between a continuous phase separating magma clasts and a dispersed phase in individual bubbles within the clasts. As regards flow behavior, it is the former, continuous, gas phase which matters, and we show that its amount is determined by the fragment size. Analysis of 25 fall deposits and 37 flow deposits demonstrates that ash and pumice populations follow a power law size distribution such that N, the number of fragments with radii larger than r, is given by N∝r−D. D values range from 2.9 to 3.9 and are always larger than 3.0 in fall deposits. D values for pyroclastic flow deposits are systematically smaller than those of fall deposits. We show that at fragmentation the amount of continuous gas phase is an increasing function of the D value. Large D values cannot be attributed to a single fragmentation event and are due to secondary fragmentation processes. Laboratory experiments on bubbly magma and on solid pumice samples demonstrate that primary breakup leads to D values of 2.5±0.1 and that repeated fragment collisions act to increase the D value. A model for size‐dependent refragmentation accounts for the observations. We propose that in a volcanic conduit, fragmentation proceeds as a sequence of events. Primary breakup releases a small amount of gas and is followed by fragment collisions. Due to refragmentation and decompression, both the mass and volume fractions of continuous gas increase. The final D value, and hence the mass fraction of continuous gas at the vent, depends on the time spent between primary fragmentation and eruption out of the vent.
Time variability of the Earth's gravity field: Hydrological and oceanic effects and their possible detection using GRACE
Authors: Wahr John , Molenaar Mery , Bryan Frank
Published: February 2004

The GRACE satellite mission, scheduled for launch in 2001, is designed to map out the Earth's gravity field to high accuracy every 2–4 weeks over a nominal lifetime of 5 years. Changes in the gravity field are caused by the redistribution of mass within the Earth and on or above its surface. GRACE will thus be able to constrain processes that involve mass redistribution. In this paper we use output from hydrological, oceanographic, and atmospheric models to estimate the variability in the gravity field (i.e., in the geoid) due to those sources. We develop a method for constructing surface mass estimates from the GRACE gravity coefficients. We show the results of simulations, where we use synthetic GRACE gravity data, constructed by combining estimated geophysical signals and simulated GRACE measurement errors, to attempt to recover hydrological and oceanographic signals. We show that GRACE may be able to recover changes in continental water storage and in seafloor pressure, at scales of a few hundred kilometers and larger and at timescales of a few weeks and longer, with accuracies approaching 2 mm in water thickness over land, and 0.1 mbar or better in seafloor pressure.
Climate variability and Ross River virus transmission in Townsville Region, Australia, 1985–1996
Authors: Tong Shilu , Hu Wenbiao , McMichael A. J.
Published: February 2004

Background  How climate variability affects the transmission of infectious diseases at a regional level remains unclear. We assess the impact of climate variation on the Ross River virus (RRv) transmission in the Townsville region, Queensland, north‐east Australia.

Methods  We obtained population‐based information on monthly variations in RRv cases, climatic factors, sea level, and population growth between 1985 and 1996. Cross‐correlations were computed for a series of associations between climate variables (rainfall, maximum temperature, minimum temperature, relative humidity and high tide) and the monthly incidence of RRv disease over a range of time lags. We assessed the impact of climate variability on RRv transmission using the seasonal auto‐regressive integrated moving average (SARIMA) model.

Results  There were significant correlations of the monthly incidence of RRv to rainfall, maximum temperature, minimum temperature and relative humidity, all at a lag of 2 months, and high tide in the current month. The results of SARIMA models show that monthly average rainfall (β = 0.0007, P = 0.01) and high tide (β = 0.0089, P = 0.04) were significantly associated with RRv transmission and maximum temperature was also marginally significantly associated with monthly incidence of RRv (β = 0.0412, P = 0.07), although relative humidity did not seem to have played an important role in the Townsville region.

Conclusions  Rainfall, high tide and maximum temperature were likely to be key determinants of RRv transmission in the Townsville region.
Seroepidemiology of dengue in the adult population of Singapore
Authors: Wilder‐Smith Annelies , Foo Winnie , Earnest Arul , Sremulanathan Sangeetha , Paton Nicholas I.
Published: February 2004

Urbanization is one of the reasons for the resurgence of dengue in tropical and subtropical countries. We conducted a cross‐sectional seroepidemiological study in Singapore to determine the extent at which the Singapore population has been exposed to dengue infections. Dengue antibodies were measures with PanBio Dengue. Of 298 enrolled subjects (age 18–45), 133 (45%) had a positive dengue serology. In multivariate analysis, age and nationality (Singaporean vs non‐Singaporean Asians) were found to be significant independent predictors. The odds ratio of dengue seroprevalence increased by 4.13 (95% CI: 2.88–5.93) for every 10 year increase in age. Dengue infections remain a major problem in Singapore.
Anaemia in pregnancy and infant mortality in Tanzania
Authors: Marchant Tanya , Schellenberg Joanna Armstrong , Nathan Rose , Abdulla Salim , Mukasa Oscar , Mshinda Hassan , Lengeler Christian
Published: February 2004

Tanzania is an area of moderate to high risk for severe anaemia during pregnancy. There is extensive literature examining the consequences of severe anaemia for pregnant women, but the impact this problem has on their infants in malaria‐endemic regions is poorly understood. Between 1999 and 2001 we used a demographic surveillance system in the Kilombero Valley, Tanzania to link morbidity and socio‐economic status data for 301 pregnant women to the survival of 365 days of their singleton babies, looking for evidence of an association between infant mortality and maternal haemoglobin (Hb). The hazards ratio for infant mortality amongst women who had been severely anaemic in pregnancy (Hb < 8 g/dl) was 3.1 [95% confidence interval (CI) 1.1–9.1, P = 0.04] compared with women with Hb above this level after controlling for other factors. Prevention of anaemia in pregnancy may lead to an improvement in infant survival.
Artemether‐lumefantrine for uncomplicated malaria: a systematic review
Authors: Omari Aika A. , Gamble Carrol , Garner Paul
Published: February 2004

Background  The World Health Organization (WHO) is promoting artemether‐lumefantrine for treating uncomplicated malaria. The objective of this review is to summarize available evidence of its effects compared with other antimalarial regimens.

Methods  We sought randomized and quasi‐randomized studies comparing artemether‐lumefantrine with any other antimalarial drug regimen. Databases searched were MEDLINE (to February 2003), EMBASE (to February 2003), and the Cochrane Controlled Trials Register (issue 1, 2003). Conference proceedings and reference article lists were searched and malaria researchers and the drug manufacturer were contacted. Two reviewers independently applied inclusion criteria and extracted data.

Results  Six trials (1698 participants) studied the four‐dose regimen. Fever and parasite clearance tended to be shorter with artemether‐lumefantrine, but parasitological failure on day 28 was more common with artemether‐lumefantrine in comparison with mefloquine (one trial, n = 233), halofantrine (one trial, n = 86) and mefloquine‐artesunate (one trial, n = 537); but less common with chloroquine (two trials, n = 378). For the six‐dose regimen, two studies compared artemether‐lumefantrine with mefloquine‐artesunate, but there was insufficient data to demonstrate any meaningful comparative effects for day 28 parasitaemia, and no difference in parasite or fever clearance time was detected. There were 11 parasitological failures with artemether‐lumefantrine and none with mefloquine‐artesunate.

Conclusion  There is no evidence to demonstrate the four‐dose regimen of artemether‐lumefantrine results in a higher cure rate than other antimalarial regimens against which it has been tested, apart from chloroquine in areas with high chloroquine resistance. Artemether‐lumefantrine has potential advantages over non‐artemisinin regimens because of the faster clearance time and gametocyte clearance. There is insufficient evidence about the six‐dose regimen to know whether it is less or more effective than current antimalarial drug regimens.
Research for control: the onchocerciasis experience*
Authors: Remme Jan H. F.
Published: February 2004

Onchocerciasis control has been very successful in Africa and research has played a critical role. An overview of the main epidemiological and implementation research activities undertaken over the last 20 years in collaboration with the African onchocerciasis control programmes and of the impact this research had on control is given. The research included the development of epidemiological modelling and its application in programme evaluation and operational planning, research on disease patterns and disease burden in different bioclimatic zones to justify and guide control operations, community trials of ivermectin to determine its safety for large‐scale use and its impact on transmission, rapid assessment methods to identify target communities for treatment and community‐directed treatment for sustained drug delivery. Lessons learned during this unique collaboration between research and control are discussed.
Use of intermittent presumptive treatment and insecticide treated bed nets by pregnant women in four Kenyan districts
Authors: Guyatt H. L. , Noor A. M. , Ochola S. A. , Snow R. W.
Published: February 2004

The roll back malaria (RBM) movement promotes the use of insecticide‐treated bednets (ITNs) and intermittent presumptive treatment (IPT) of malaria infection as preventive measures against the adverse effects of malaria among pregnant women in Africa. To determine the use of these preventive measures we undertook a community‐based survey of recently pregnant women randomly selected from communities in four districts of Kenya in December 2001. Of the 1814 women surveyed, only 5% had slept under an ITN. More than half of the 13% of women using a bednet (treated or untreated) had bought their nets from shops or markets. Women from rural areas used bednets less than urban women (11%vs. 27%; P < 0.001), and 41% of the bednets used by rural women had been obtained free of charge from a research project in Bondo or a nationwide UNICEF donation through antenatal clinics (ANCs). Despite 96% of ANC providers being aware of IPT with sulphadoxine–pyrimethamine (SP), only 5% of women interviewed had received two or more doses of SP as a presumptive treatment. The coverage of pregnant women with at least one dose of IPT with SP was 14%, though a similar percentage also had received at least a single dose as a curative treatment. The coverage of nationally recommended strategies to prevent malaria during pregnancy during 2001 was low across the diverse malaria ecology of Kenya. Rapid expansion of access to these services is required to meet international and national targets by the year 2005. The scaling up of malaria prevention programmes through ANC services should be possible with 74% of women visiting ANCs at least twice in all four districts. Issues of commodity supply and service costs to clients will be the greatest impediments to reaching RBM targets.
Epigenetic inheritance of fetal genes in allergic asthma
Authors: Bousquet J. , Jacot W. , Yssel H. , Vignola A. M. , Humbert M.
Published: February 2004

Asthma has been associated with an exaggerated T‐helper type 2 (Th2) over Th1 responses to allergic and nonallergic stimuli, which leads to chronic airway inflammation and airway remodeling. In the present article, we propose that many of the genes involved in IgE synthesis and airways (re)modeling in asthma are persistent or reminiscent fetal genes which may not be silenced during early infancy (or late pregnancy). Genes of the embryologic differentiation of ectodermic and endodermic tissues may explain some of the patterns of airway remodeling in asthma. In utero programming leads to gene expression, the persistence of which may be associated with epigenetic inheritance phenomena induced by nonspecific environmental factors. Clear delineation of these issues may yield new information on the mechanisms of asthma and new targets for therapeutic intervention and primary prevention.
Asthma and atopy – the price of affluence?
Authors: Von Hertzen L. C. , Haahtela T.
Published: February 2004

Irrespective of improved knowledge of many aspects of atopic diseases, the unfavorable trends in their prevalence particularly among children could not have been reversed. A growing body of evidence suggests that something may lack from our societal affluence that has the capacity to provide protection against the development of atopic diseases. Much attention during the last years has been devoted to the hygiene hypothesis. This review outlines the impact of environment and lifestyle, particularly from the perspective of the East–West gradient, on the development of atopic diseases, with a special emphasis on the hygiene hypothesis in its broadest sense.
CARRIER CONCENTRATION PROFILES OF ION-IMPLANTED SILICON
Authors: Bader R. , Kalbitzer S.
Published: February 2004

Sheet-resistivity and Hall-effect measurements on ion-implanted silicon wafers have been performed. Carrier concentration profiles over the range of about 1019–1011 carriers/cm3 have been obtained for implants of 1014 ions/cm2 of 11B, 27Al, and 31P. Three regions, due to different penetration mechanisms, can be clearly distinguished: the amorphous range, the channeling range, and the supertail. Some indication for a kinetic substitution mechanism is seen in the channeling region.
TEMPERATURE-DEPENDENT ATTENUATION OF ULTRASONIC SURFACE WAVES IN QUARTZ
Authors: Daniel M. R. , de Klerk J.
Published: February 2004

The attenuation of Rayleigh waves in quartz was measured as a function of temperature from 4.2 to 100 °K and frequency from 300 to 2000 MHz. Below 20 °K, the attenuation was observed temperature-independent. From 20 to 40 °K, the results were consistent with a three-phonon interaction process varying as T4 but with little or no dependence on frequency. Above 40 °K, the attenuation showed a lower dependence on temperature than T4 and oscillated due to an interference effect between the Rayleigh wave and a bulk wave generated at the same time.
OPTICAL PROBING OF ACOUSTIC SURFACE-WAVE HARMONIC GENERATION
Authors: Lean E. G. H. , Tseng C. C. , Powell C. G.
Published: February 2004

The growth of nonlinearly generated harmonics of acoustic surface waves in LiNbO3 substrates has been observed directly by an optical probe. The attenuation of acoustic surface waves as a function of the level of input power and loss of energy to the nonlinearly generated harmonics is measured. The large nonlinear coupling to the high harmonics of surface acoustic waves, which is an encouraging sign for parametric amplification, may impose some limitations on linear devices at high power levels.
REDUCTION OF PENUMBRA IN X-RAY IMAGES BY OPTICAL SPATIAL FILTERING
Authors: Krusos G. A. , Hilal S. K. , Seaman W. B. , Myers G. H.
Published: February 2004

The finite size of the focal spot of an x-ray tube produces a penumbra in x-ray images. Optical spatial-filtering techniques are being developed to compensate for penumbral effects in medical x-ray photographs and thereby improve the contrast and resolution. The first known successful results on x-ray images are described.
TRANSIENT HIGH-DENSITY INJECTION IN A SEMICONDUCTOR WITH TRAPS
Authors: Ancker-Johnson Betsy , Robbins William P. , Chang David B.
Published: February 2004

The properties of high-density injection into p-InSb at 77 °K are compared with theory. An extension of Dean's theory is in satisfactory agreement with the extensive observations which include density-dependent growth times.
INTERACTION BETWEEN B ATOMS AND DEFECTS PRODUCED BY Hg BOMBARDEMENT IN SILICON
Authors: Mea G. Della , Drigo A. V. , Mazzoldi P. , Nardelli G. , Zannoni R.
Published: February 2004

The lattice disorder produced by 42-keV Hg ions implanted in B-doped Si at room temperature has been measured by means of the channeling and of the backscattering of 2-MeV He ions. An annealing effect connected to B concentration is observed.
COMPARISON OF HF AND DF CONTINUOUS CHEMICAL LASERS: I. POWER
Authors: Spencer Donald J. , Mirels Harold , Jacobs Theodore A.
Published: February 2004

A continuous DF chemical laser is reported. Population inversion is obtained by diffusing D2 into a supersonic free jet containing F atoms. Output power of the DF laser is compared with a similar HF laser previously reported. The ratio of DF to HF laser output power is 0.7 for fixed supersonic jet conditions and the same molar flow of H2 and D2. The efficiency of conversion of chemical energy to laser energy is approximately 12 and 8 % for the HF and DF lasers, at power levels of 475 and 340 W, respectively.
POPULATION INVERSION BETWEEN ΔMF = 0 HYPERFINE SUBLEVELS OF RUBIDIUM AND CESIUM
Authors: Franz F. A.
Published: February 2004

Optical pumping of Rb or Cs subject to relaxation through the formation of relatively long-lived alkali-rare-gas molecular complexes is shown to yield a unique distribution of population throughout the magnetic sublevels of the alkali ground state. Large overpopulations of the sublevels of the upper hyperfine state are obtained for a particular range of the ratio of pumping rate to relaxation rate. The technique may make feasible the construction of a Cs maser.
NEW HIGH INTENSITY ION SOURCE WITH VERY LOW EXTRACTION VOLTAGE
Authors: Geller R.
Published: February 2004

A new ion source is described, which produces slow ion beams of I+> 10−2 A cm−2 with extraction voltages Vextr ≳ 102 V and a relatively small spread.
HOT-HOLE ANISOTROPY IN SILICON
Authors: Quaranta A. Alberigi , Canali C. , Ottaviani G.
Published: February 2004

Experimental results on the hole drift mobility in silicon are presented. The electric field is applied parallel to the <111> and <100> crystallographic directions at four different temperatures between 77 and 300°K. The measurements have been performed with the time-of-flight technique. Experimental evidence is given for the first time of anisotropy of drift velocity of holes at intermediate and high electric fields.
EPITAXIAL LEAD SULFIDE PHOTOVOLTAIC CELLS AND PHOTOCONDUCTIVE FILMS
Authors: Schoolar Richard B.
Published: February 2004

Single-crystal lead sulfide photovoltaic cells and photoconductive films were prepared using epitaxial growth techniques. The spectral response of the photovoltaic cells is characterized by a sharp peak at wavelengths just short of the energy gap of PbS. The photoconductive films were grown with carrier concentrations as low as 3×1016 cm−3 and exhibit two large, distinct photoconductive signals when cooled to 77 °K. One response is characterized by a time constant > 50 msec and is attributed to photoexcitation of electrons from oxygen-induced surface traps. The second response has a time constant of 32 μ sec and is attributed to intrinsic photoconductivity of lead sulfide.
Na-INDUCED FACETTING OF W(112)
Authors: Chen J. M.
Published: February 2004

The effects of Na adsorption on an oxygen-covered W(112) surface are reported. It is found that if a W(112) surface is first covered with 1.5 monolayers of atomic oxygen and then covered with 0.8 monolayer of Na, and the surface is then heated in vacuum to 650 °K and higher, a series of surface structures is observed. These structures can only be explained by assuming facetting of the W(112) surface.
MEASUREMENT OF THE UPPER LASER LEVEL LIFETIME IN THE HELIUM-CADMIUM LASER BY FAST CAVITY DUMPING TECHNIQUES
Authors: Klein M. B. , Maydan D.
Published: February 2004

The upper level lifetime for the 4416-Å transition in the helium-cadmium laser has been measured to be 670 ± 70 nsec. The measurements were accomplished by rapidly removing the intracavity laser power while monitoring the sidelight emission from the discharge at the laser wavelength. This measurement technique is applicable to other laser systems with upper level lifetimes which are long compared with the cavity dumping time, and has the advantage of providing a direct measurement of the upper level lifetime.
HIGH-RESOLUTION ELECTRON MICROSCOPE IMAGES OF CRYSTAL LATTICE PLANES USING CONICAL ILLUMINATION
Authors: Heinemann Klaus , Poppa Helmut
Published: February 2004

The (111)-, (200)-, and (220)-lattice planes of small vapor-deposited gold crystals with 2.35-, 2.04-, and 1.44-Å respective interplanar lattice spacings were resolved by high-resolution transmission electron microscopy. The simultaneous resolution in one micrograph of the three different lattice spacings and the elimination of azimuthal orientation preferences of the imaged lattice planes were achieved by using conical instead of axial specimen illumination methods.
NONLINEAR OPTICAL PROPERTIES OF Ag3SbS3
Authors: Gandrud W. B. , Boyd G. D. , McFee J. H. , Wehmeier F. H.
Published: February 2004

The nonlinear optical properties of Ag3SbS3 (pyrargyrite) as determined by second harmonic generation (SHG) with the 10.6μ CO2 laser are presented. Phase-matched nonlinear mixing is possible and the material is suitable as a phase-matched standard in the infrared for optical nonlinearities.
COMMENTS ON MICROWAVE SCATTERING FROM ANISOTROPIC PLASMA TURBULENCE
Authors: Bugnolo Dimitri S.
Published: February 2004

Some comments are directed towards a recent paper on the subject of microwave scattering by a well underdense anisotropic weakly ionized turbulent plasma.
THRESHOLD SWITCHING AND THERMAL FILAMENTS IN AMORPHOUS SEMICONDUCTORS
Authors: Weirauch Donald F.
Published: February 2004

Threshold switching in a thick specimen of an amorphous semiconductor was studied. With the aid of an infrared viewer, the existence of a thermal filament during switching was confirmed. By spectral analysis, the temperature of this filament was estimated to be between 650 and 800 °C. No crystals were observed in the nonoxide glass, either before or after switching had occurred.
PROBING OF ELASTIC SURFACE WAVES IN PIEZOELECTRIC MEDIA
Authors: Richardson B. A. , Kino G. S.
Published: February 2004

Data are presented which indicate that detection of the rf electrical potential associated with an acoustic surface wave in a piezoelectric medium by a simple point probe can yield extensive information about the propagation characteristics of such waves. Such a probe, in mechanical contact with the propagating surface of a 107-MHz LiNbO3 delay line, has been used to measure the diffraction pattern of the acoustic energy, spreading of the acoustic beam, insertion loss due to misalignment of the transducer axis with the crystal symmetry axis, and the amplitude and phase variations of the acoustic wave near the output transducer.
VACANCY CLUSTERS IN DISLOCATION-FREE SILICON
Authors: de Kock A. J. R.
Published: February 2004

Dislocation-free silicon crystals made by the floating zone technique contain vacancy clusters formed during cooling of the crystal after growth. The distribution and concentration of these defects have been determined. A model is presented describing the formation of these clusters. The influence of vacancy clusters on the leakage current of planar diodes is investigated.
DEPTH DISTRIBUTION OF EPR CENTERS IN 400-keV O+ ION-IMPLANTED SILICON
Authors: Brower K. L. , Vook F. L. , Borders J. A.
Published: February 2004

The depth distribution of Si-P3 centers in 400-keV O+ ion-implanted silicon was determined using EPR measurements in conjunction with anodization and stripping of the implanted layer. The depth distribution of the EPR centers compares favorably to theoretical calculations by Brice for the depth distribution of the energy deposited into atomic processes and with infrared absorption measurements of the depth distribution of divacancies by Stein, Vook, and Borders. The combined EPR and infrared measurements indicate that the Fermi level in the damaged layer lies between Ec − 0.21 eV and Ev + 0.25 eV.
ULTRAFAST RISE TIME LASER-INDUCED STRESS WAVES
Authors: Peercy P. S. , Jones E. D. , Bushnell J. C. , Gobeli G. W.
Published: February 2004

Stress pulses having rise times ≲ 1 nsec have been produced at the surfaces of solids. These were produced by the absorption of single laser pulses of time durations of ∼ 3 psec and energies up to 20 J.
SPONTANEOUS SINGLE-FREQUENCY OUTPUT FROM A SPATIALLY HOMOGENEOUS Nd:YAG LASER
Authors: Danielmeyer H. G. , Nilsen W. G.
Published: February 2004

By moving a Nd:YAG rod relative to the cavity field with velocities of the order of centimeters per second, we obtained single-frequency oscillation close to the center of the gain curve with output powers up to 1.2 W. Our results can be understood quantitatively by considering the smoothing effect of the relative motion on the spatial distribution of the population inversion.
ELECTRON TUNNELING INTO AMORPHOUS GERMANIUM
Authors: Osmun J. W. , Fritzsche H.
Published: February 2004

Al–Al2O3–Ge tunnel junctions were prepared to study electron tunneling into amorphous germanium films. An almost symmetric conductance minimum centered at zero bias without additional structure was observed. The change in conductance from 1V to zero bias is 103 at 78°K and about 102 at 300°K. The zero bias conductance is 102 times lower at 78°K than at 300°K. The results indicate a large density of states in the gap or near the surface.
DIFFERENTIAL DOPPLER VELOCITY MEASUREMENTS
Authors: Penney C. M.
Published: February 2004

Observed signal characteristics and measurement accuracy are described for a recently developed noncontacting optical velocity sensing method as applied to extended moving surfaces. This method is based on an optical heterodyne measurement of the difference between two Doppler shifts which are produced in the light scattered through two different angles by the moving surface. It provides convenient measurements of velocity components tangent to extended surfaces that are optically rough. Absolute accuracies to at least 0.1%, and relative accuracies to 0.04% are reported.
ELECTRON PARAMAGNETIC RESONANCE OF ION-IMPLANTED DONORS IN SILICON
Authors: Brower K. L. , Borders J. A.
Published: February 2004

The EPR of As75, Sb121, and Sb123 substitutional donors implanted in silicon have been observed. The Si-P3 and Si-P1 center resonances associated with the damage were also observed. Samples were implanted at room temperature to fluences of ∼ 1013 ions/cm2, and the EPR spectra associated with the damage and the implanted impurities were monitored as the samples were isochronally annealed to 970 °C. The spectra of the implanted donors were observed after the 400 °C anneal with illumination and following the 600 °C anneal without illumination. After the anneal at ∼ 900 °C, the proportion of implanted antimony that is observed by EPR to be substitutional is significantly larger than for the implanted arsenic.
CHEMICAL EFFECTS ON THE KLL AUGER ELECTRON SPECTRUM FROM SURFACE CARBON
Authors: Haas T. W. , Grant J. T.
Published: February 2004

It is found that the KLL carbon Auger spectrum is strongly influenced by the chemical state of the carbon. This is expected since the L electrons in carbon are the valence electrons. We have found that it is possible to distinguish between surface carbon and adsorbed CO on the basis of this carbon Auger spectrum. This sensitivity to the chemical state of the emitting atom when the Auger electron is ejected from the valence band suggests that this measurement may be useful in determining bonding of surface atoms.
PIEZOELECTRIC SURFACE WAVES IN CUBIC AND ORTHORHOMBIC CRYSTALS
Authors: Tseng C.-C.
Published: February 2004

The existence of a piezoelectric surface wave, which does not arise in nonpiezoelectric materials has been reported in hexagonal crystals by Bleustein and Gulyaev. In this letter, similar waves are reported to exist in cubic crystals of 23 and 4̄3m classes and orthorhombic crystals of mm2 class. Velocity equations for the piezoelectric surface waves in these symmetry classes are presented. It has been demonstrated that the velocities are always smaller than the piezoelectrically stiffened but always larger than the unstiffened bulk shear waves in the corresponding direction of propagation. Numerical results for the particular examples of Bi12GeO20(23) and Ba2NaNb5O15(mm2) are also presented.
FREQUENCY DEPENDENCE OF THE DEBYE LENGTH IN COMPENSATED EXTRINSIC PHOTOCONDUCTORS
Authors: Milton A. Fenner
Published: February 2004

A frequency-dependent Debye length is derived for the case of unipolar photoconductivity in a compensated extrinsic photoconductor. The frequency dependence is associated with the finite time necessary to establish equilibrium between an excess free carrier density and a deficit ionized impurity density in the case of bipolar recombination. The frequency dependence of the Debye length leads to a frequency-dependent effective drift length Leff(ω)=Eμ {1τρ[1+n0p0′(1+ω2τ2n02p02)] +ω2τ (n0p0)2(1+ ω2 τ2n02p02)−1}−1 (p type)which can be used to explain the sweepout results obtained by Williams with mercury-doped germanium photoconductors under high resistivity conditions.