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Background Syringe services programs (SSPs) are effective venues for delivering harm-reduction services to people who inject drugs (PWID). However, SSPs often face significant barriers to implementation, particularly in the absence of known human immunodeficiency virus (HIV) outbreaks. Methods Using an agent-based model, we simulated HIV transmission in Scott County, Indiana, a rural county with a 1.7% prevalence of injection drug use. We compared outcomes arising in the absence of an SSP, in the presence of a pre-existing SSP, and with implementation of an SSP after the detection of an HIV outbreak among PWID over 5 years following the introduction of a single infection into the network. Results In the absence of an SSP, the model predicted an average of 176 infections among PWID over 5 years or an incidence rate of 12.1/100 person-years. Proactive implementation averted 154 infections and decreased incidence by 90.3%. With reactive implementation beginning operations 10 months after the first infection, an SSP would prevent 107 infections and decrease incidence by 60.8%. Reductions in incidence were also observed among people who did not inject drugs. Conclusions Based on model predictions, proactive implementation of an SSP in Scott County had the potential to avert more HIV infections than reactive implementation after the detection of an outbreak. The predicted impact of reactive SSP implementation was highly dependent on timely implementation after detecting the earliest infections. Consequently, there is a need for expanded proactive SSP implementation in the context of enhanced monitoring of outbreak vulnerability in Scott County and similar rural contexts.

BACKGROUND: Pre-exposure prophylaxis (PrEP) uptake has been slow among African American men who have sex with men (AAMSM) in the United States. We used an agent-based model (ABM) to simulate race-specific PrEP coverage to estimate their impact on racial disparities in HIV incidence among MSM in Atlanta, Georgia. METHODS: An ABM was constructed to simulate HIV transmission in a dynamic network of 10,000 MSM over ten years, beginning in 2015. We modeled a base scenario with estimated PrEP coverage of 2.5% among AAMSM and 5.0% among white MSM (WMSM). We then compared HIV incidence over ten years and calculated a disparity ratio of AAMSM to WMSM incidence rates across varying PrEP scale-up scenarios, with equal and unequal coverage among AAMSM and WMSM. RESULTS: Assuming current coverage remains constant, the model predicts HIV incidence rates of 2.95 and 1.76 per 100 person-years among AAMSM and WMSM respectively, with a disparity ratio of 1.68. If PrEP coverage were to increase six-fold without addressing inequities in PrEP uptake, the model predicts incidences of 2.65 and 1.34, corresponding to a mean decrease of 10.4% and 24.0% in HIV incidence, respectively. This stronger benefit for WMSM increased the disparity ratio to 1.98. Equal PrEP coverage among AAMSM and WMSM resulted in lower incidence rates overall with lower disparity ratios. CONCLUSION: Lower uptake among AAMSM relative to WMSM may limit the population-level impact of PrEP use among AAMSM, which may ultimately culminate in wider racial disparities in HIV incidence among MSM.

Little is known about the potential population-level impact of HIV pre-exposure prophylaxis (PrEP) use among cisgender male sex workers (MSWs), a high-risk subset of cisgender men who have sex with men (MSM). Using an agent-based model, we simulated HIV transmission among cisgender MSM in Rhode Island to determine the impacts of PrEP implementation where cisgender MSWs were equally (“standard expansion”) or five times as likely (“focused expansion”) to initiate PrEP compared to other cisgender MSM. Without PrEP, the model predicted 920 new HIV infections over a decade, or an average incidence of 0.39 per 100 person-years. In a focused expansion scenario where 15% of at-risk cisgender MSM used PrEP, the total number of new HIV infections was reduced by 58.1% at a cost of $57,180 per quality-adjusted life-year (QALY) gained. Focused expansion of PrEP use among cisgender MSWs may be an efficient and cost-effective strategy for reducing HIV incidence in the broader population of cisgender MSM.

Summary The burden of HIV/AIDS and other transmissible diseases is higher in prison and jail settings than in the non-incarcerated communities that surround them. In this comprehensive review, we discuss available literature on the topic of clinical management of people infected with HIV, hepatitis B and C viruses, and tuberculosis in incarcerated settings in addition to co-occurrence of one or more of these infections. Methods such as screening practices and provision of treatment during detainment periods are reviewed to identify the effect of community-based treatment when returning inmates into the general population. Where data are available, we describe differences in the provision of medical care in the prison and jail settings of low-income and middle-income countries compared with high-income countries. Structural barriers impede the optimal delivery of clinical care for prisoners, and substance use, mental illness, and infectious disease further complicate the delivery of care. For prison health care to reach the standards of community-based health care, political will and financial investment are required from governmental, medical, and humanitarian organisations worldwide. In this review, we highlight challenges, gaps in knowledge, and priorities for future research to improve health-care in institutions for prisoners.

BackgroundIncarceration and HIV disproportionately impact African American communities. The mass incarceration of African American men is hypothesized to increase HIV acquisition risk for African American women. Interventions optimizing HIV care engagement and minimizing sexual risk behaviors for men living with HIV post-incarceration may decrease HIV incidence.MethodsUsing an agent-based model, we simulated a sexual and injection drug using network representing the African American population of Philadelphia. We compared intervention strategies for men living with HIV post-incarceration by the number of averted HIV transmissions to women within the community. Three interventions were evaluated: a 90-90-90 scenario scaling up HIV testing, ART provision, and ART adherence; a behavioral intervention decreasing sexual risk behaviors; and a combination intervention involving both.ResultsThe status quo scenario projected 2,836 HIV transmissions to women over twenty years. HIV transmissions to women decreased by 29% with the 90-90-90 intervention, 23% with the behavioral intervention, and 37% with both. The number of men living with HIV receiving the intervention needed in order to prevent a single HIV transmission ranged between 6 and 10.ConclusionInterventions to improve care engagement and decrease sexual risk behaviors post-incarceration for men living with HIV have the potential to decrease HIV incidence within African American heterosexual networks.

Summary Background Oral pre-exposure prophylaxis (PrEP) prevents HIV infection in men who have sex with men (MSM); however, adherence is an ongoing concern. Long-acting injectable PrEP is being tested in phase 3 trials and could address challenges associated with adherence. We examined the potential effectiveness of long-acting injectable PrEP compared with oral PrEP in MSM. Methods We used an agent-based model to simulate HIV transmission in a dynamic network of 11 245 MSM in Atlanta, GA, USA. We used raw data from studies in macaque models and pharmacokinetic data from safety trials to estimate the time-varying efficacy of long-acting injectable PrEP. The effect of long-acting injectable PrEP on the cumulative number of new HIV infections over 10 years (2015–24) was compared with no PrEP and daily oral PrEP across a range of coverage levels. Sensitivity analyses were done with varying maximum efficacy and drug half-life values. Findings In the absence of PrEP, the model predicted 2374 new HIV infections (95% simulation interval [SI] 2345–2412) between 2015 and 2024. The cumulative number of new HIV infections was reduced in all scenarios in which MSM received long-acting injectable PrEP compared with oral PrEP. At a coverage level of 35%, compared with no PrEP, long-acting injectable PrEP led to a 44% reduction in new HIV infections (1044 new infections averted [95% SI 1018–1077]) versus 33% (792 infections averted [763–821]) for oral PrEP. The relative benefit of long-acting injectable PrEP was sensitive to the assumed efficacy of injections received every 8 weeks, discontinuation rates, and terminal drug half-life. Interpretation Long-acting injectable PrEP has the potential to produce larger reductions in HIV transmission in MSM than oral PrEP. However, the real-world, population-level impact of this approach will depend on uptake of this prevention method and its effectiveness, as well as retention of patients in clinical care. Funding National Institute on Drug Abuse and National Institute of Mental Health.

Phytopathogens deliver effector proteins inside host plant cells to promote infection. These proteins can also be sensed by the plant immune system, leading to restriction of pathogen growth. Effector genes can display signatures of positive selection and rapid evolution, presumably a consequence of their co-evolutionary arms race with plants. The molecular mechanisms underlying how effectors evolve to gain new virulence functions and/or evade the plant immune system are poorly understood. Here, we report the crystal structures of the effector domains from two oomycete RXLR proteins, Phytophthora capsici AVR3a11 and Phytophthora infestans PexRD2. Despite sharing

Magnetic anisotropy measurements have been made on fifty-four oriented samples from the Carna and Screeb areas of the Galway Granite, and from the Ardara pluton and the Main Granite (including the Trawenagh Bay Granite) in Donegal. The origin of magnetic anisotropy in plutonic magnetic rocks is discussed, and it is concluded that it is probably due to grain alignment of inequant magnetite, which may occur either as free grains or as secondary inclusions in ferromagnesian minerals. The grain alignment may occur either whilst the magma is essentially fluid, giving a magnetic lineation transverse to the flow, or at a much later stage of consolidation during plastic deformation, in which case the magnetic lineation parallels the direction of greatest elongation. The results of the measurements are consistent with macroscopic foliations and lineations where these have been observed, but also indicate the existence of fabrics too weak to observe by conventional methods. This is because the magnetic method assesses the alignment of a very large number of grains, and is therefore much more sensitive than conventional fabric analysis. The weak fabrics can be qualitatively explained in terms consistent with other evidence relating to the emplacement of the granites, and experimental work now in progress may make possible a more quantitative interpretation.

Gravity and seismic surveys over the estuaries of the rivers Dovey, Dysynni, Glaslyn and Mawddach have indicated that the rock floor lies at depths of from 100 to 1,250 ft (30 m to 380 m) below the present surface. The methods of survey and difficulties of interpretation are discussed, and the significance of the results is assessed in conjunction with those already published for the Teifi estuary and with preliminary results obtained by seismic reflection profiling in. Cardigan Bay. It is concluded that all the valleys with the exception of the Glaslyn could have been carved during Pleistocene times, but that the much deeper buried valley of the Glaslyn, extending south of Portmadoc across Morfa Harlech, is probably of earlier origin. Des etudes sismiques et de gravie effectuees dans les estuaires des rivieres Dovey, Dysynni, Glaslyn and Mawddach ont indique que la plateforme rocheuse se trouve a des profondeurs de 100 ft (30,5 m) a 1 250 ft (380 m) au—desous de la surface actuelle. Les methodes d'etude et les difficultes d'interpretation sont discutees et la signification des resultats est evaluee en conjonction avec ceux deja publices pour l'estuaire de la Teifi et avee les resultats obtenus par profiles de reflexion sismique de la Baie de Cardigan. On en a conch que toutes les vallees a l'exception de la Glaslyn auraient pu ětre taillees a la periode Pleistocene, mais que la Vallee de la Glaslyn enfouie beaucoup plus profondement qui s'etend au sud de Portmadoc a travers Morfa Harlech, est probablement d'origine plus ancienne.

Miller production began its decline phase in July 1997. To investigate the challenges of the decline period and the options for extending field life a detailed reservoir heterogeneity model was set up based on analysis of 26 wells, of which 19 were cored. The Miller fan is a high net: gross sandy submarine fan system in which lobe abandonment facies and numerous thin shales form the important heterogeneities. Each reservoir zone was described in terms of eight depositional elements and fourteen lithotypes. These descriptions were incorporated into the model at a resolution which ensured capture of the most significant heterogeneities. A stochastic generator was used to build a detailed static description of the permeability of the reservoir. The important heterogeneities were captured in a cell size of 60 m × 60 m × c. 0.02 m. Volumetric rock properties such as zone isochore, net: gross and porosity were mapped using conventional methods. The static description was up-scaled into an area of local grid refinement of the Eclipse reservoir simulator with 33 dynamic subzones at a cell size of 100 m × 100 m × c. 2.5 m. The detailed reservoir model matched well and field performance in the decline period more closely than the previous deterministic model. Stochastic realizations of the model enabled a better estimate of uncertainty to be demonstrated. The success of the process indicated that greater benefit would be obtained by its extension over a larger area of the field.

Over the past 20 years, Culham Laboratory has been involved in the development of ion sources. Initially these were positive ion systems using magnetic multipole sources for neutral beam heating in the fusion program. However, the development of high proton yield sources with a magnetic filter at Culham has led to a major program in negative ion sources based on the so‐called volume‐type source which has a similar design. This work has been the basis of a range of negative ion sources for industrial, defence, and fusion applications, all of which are described. A significant part of this work lies in the basic physics of these sources, both for modeling and ion beam acceleration. Numerical models of these are presented. Recently the effects of catalysts such as cesium on the discharge has been shown to cause considerable enhancement in H− and D− yield. The cesium itself also acts as a discharge component and a large source and accelerator for a pure cesium diagnostic beam has been developed. This technique is applicable to other vapors.

Recent review articles in environmental policy have called for more rigorous cross-national tests and for better integration with the standard literature on comparative politics and political economy. In this paper we take a first step in that direction, examining the relationship between air pollution and left party strength in seventeen OECD countries. Despite theoretical salience and political relevance, we know of no previous attempt of this sort. Three competing hypotheses exist. First, because of an historic agenda which emphasizes maximum employment and material welfare for the working class, left party strength might be associated with lower than normal environmental quality. Second, given the belief in government intervention to socialize the negative externalities of market capitalism, left party strength might motivate higher than normal environmental quality. Third, despite observed variations in agenda setting, policy formulation, and implementation, skeptics have often replied, "different styles, similar content", suggesting no party relevance at all. Our analysis, controlling for quantitative energy consumption and qualitative economic structure, reveals a moderate but sustainable inverse relationship between left party strength and per capita levels of air pollution. In the conclusion we speculate how and why this result might occur.

Phytopathogens deliver effector proteins inside host plant cells to promote infection. These proteins can also be sensed by the plant immune system, leading to restriction of pathogen growth. Effector genes can display signatures of positive selection and rapid evolution, presumably a consequence of their co-evolutionary arms race with plants. The molecular mechanisms underlying how effectors evolve to gain new virulence functions and/or evade the plant immune system are poorly understood. Here, we report the crystal structures of the effector domains from two oomycete RXLR proteins, Phytophthora capsici AVR3a11 and Phytophthora infestans PexRD2. Despite sharing

Measurements are made of the extracted H- ion current from a magnetic multipole volume source operating CW. Ion currents up to 44 mA have been achieved using a 16 mm diameter extraction aperture. The transported ion beam current is dependent on both the number of filaments in the source and the filament diameter. The authors present data which show that this dependency, at least for this source, is due largely to the cathode structures acting as an ion collector. As the cathode area is increased, the fraction of discharge current comprising collected ions is increased. In this source as much as 28% of the arc current may be ions drawn from the plasma. Thus comparisons at the same arc current for different cathode areas are not made with the same emitted electron current from the cathodes and hence not at the same plasma conditions. This has important implications for the arc efficiency of such discharges.

Shallow seismic reflection surveys have a range of application in groundwater investigations particularly where a precise solution to a subsurface problem is required. Recent surveys have mapped depth to bedrock, depth to water table, structure within alluvial deposits and the positions of old mineworkings. Example surveys from Down Ampney illustrate the application of shallow reflection surveys in the precise location of structural faults.

High-resolution reflection surveys have been used in watercovered areas for some time, but only during the last decade has serious attention been paid to the development of survey techniques to give comparable results on land. These techniques are now becoming well established. This paper gives an outline of the principles of reflection seismology and of the particular problems that arise when the method is applied to depths of 200 m and less.

The aims of processing shallow reflection data are no different from those established for petroleum seismology and the well known methods of this field can on the whole be adopted for high-resolution surveys. The need for rapid and economical processing is being met by the appearance of a range of PC-based packages and results can be obtained from initial data of reasonable quality which are comparable with those normal on the larger scale. This paper surveys the conventional seismic reflection processing sequence and points to some of the particular problems that can arise when it is applied to shallow data.

H−/D− current and emittance scaling is measured in a magnetic multipole negative ion source. The gas in the source is the only difference as no reoptimization of the source is carried out, thus giving a direct comparison of the performance for the two isotopes. It is found that the H− current is greater than the D− current by approximately a factor of 2 under the same discharge conditions. The extracted electron to ion ratio is commensurately higher in deuterium than in hydrogen. Finally, the emittance in deuterium at the higher arc currents is found to be lower than that in hydrogen. Some comments are made on the scaling within the context of the accepted model of negative ion production.

Two designs of electron suppressor have been tested in a volume negative ion source operating dc with a large extraction aperture diameter (16 mm). Both suppressors employ magnetic fields to divert the electrons near the extraction aperture onto collector electrodes. However, while one suppressor uses a fixed field produced by permanent magnets, the other employs a variable field produced by a solenoidal coil. These suppressors allow low values (3–4:1) of extracted electron to ion currents to be obtained. The results are compared with a diffusion model and a hydrodynamic model of the transport of the electrons across the magnetic field. They show that the hydrodynamic model gives a good description of the suppression and transport of the electrons.

An estimated 15% of global crop production is lost to pre-harvest disease every year. New ways to manage plant diseases are required. A mechanistic understanding of how plant pathogens re-program their hosts to enable colonisation may provide novel genetic or chemical opportunities to interfere with disease. One notorious plant parasite is the Irish potato famine pathogen Phytophthora infestans. This pathogen remains a considerable threat to potato/tomato crops today as the agent of late blight. Plant pathogens secrete effector proteins outside of and into plant cells to suppress host defences and manipulate cell physiology. Structural studies have provided insights into effector evolution and enabled experiments to probe function [1-3]. Crystal structures of 4 Phytophthora RXLR-type effectors, which are unrelated in primary sequence, revealed similarities in the fold of these proteins. This fold was proposed to act as a stable scaffold that supports diversification of effectors. Further, molecular modelling has enabled mapping of single-site variants responsible for specialisation of a Phytophthora Cystatin-like effector, revealing how effectors can adapt to new hosts after a "host jump". Structural studies describing how RXLR-effectors interact with host targets are lacking. We have used Y2H/co-IP studies to identify host proteins that interact with P. infestans effectors PexRD2 and PexRD54. PexRD2 interacts with MAPKKKe, a component of plant immune signalling pathways, and suppressed cell death activities of this protein. We used the structure of PexRD2 to design mutants that fail to interact with MAPKKKe, and no longer suppress cell-death activities. We found that PexRD54 interacts with potato homologues of the autophagy protein ATG8. We have obtained a crystal structure for PexRD54 in the presence of ATG8. We are now using X-ray scattering to verify the complex structure in solution prior to establishing the role of this interaction during infection.

We evaluated the effect of the Magenstrasse and Mill (MM) operation--a new form of non-banded vertical gastroplasty-on weight loss, plasma leptin levels and insulin resistance.Fasting plasma glucose, leptin and insulin levels were measured in 12 normal controls, 39 morbidly obese patients and 39 patients a median 3 years after the MM procedure. Insulin resistance was calculated by the homeostasis model insulin resistance index.Body mass index mean (s.d.) decreased significantly (p0.0001), from 48(7) to 33(5) kg/m2, after the MM procedure. Fasting plasma leptin concentration in the morbidly obese group was 37.9(15.4) ng/ml, significantly (p0.0001) higher than the control group (12.2(8.4)) and the MM group (19.1(12.7)) ng/ml. Fasting plasma insulin concentrations were also significantly (p0.0001) higher in the morbidly obese group compared with than in the MM group or in the control group: 35.5(22.3) mU/l, 15.5(7.1) mU/l and 13.6(3.4) mU/l, respectively. Insulin resistance was 9.6(7.2) in the morbidly obese group and 3.5(1.9) in the MM group (p0.0001).This is one of the first studies to show that the decrease in insulin resistance after weight loss achieved by anti-obesity surgery is associated with significantly lower levels of plasma leptin.

The plasma characteristics of a volume negative ion source are described. An indirect measurement of the negative ion current density in the source has been made. Beam extraction measurements are used to attempt to verify the measurement in the source. The two are found to be in proportion. The difference between the two is briefly discussed.

Two distinctive techniques have been developed to deliver a quantifiable dose of cesium to a volume ion source. The first method uses alkali metal dispensers in the form of thin metal wires, and the second method allows cesium to be dispensed repeatedly up to a total inventory of ∼8 g. This paper reports on the testing of these devices on two volume ion sources, and details the effects that cesium has on the extracted negative ion current and the plasma parameters. In addition, comparisons are made between the surface production model for cesium enhancement, and a volume or collisional model.

A review is given of progress in ion source performance at the cw test stand. Data is presented both for pure and cesiated source performance. For uncesiated operation we show how the performance depends on cathode area by changing both filament number and diameter. We have proved that this is due to the collection of ions from the plasma by the cathode structure. Through the use of cesium in the ion source the H− and D− current is enhanced by about a factor of two. An accelerator perveance limit was identified which prevented all the current available from the source being transported, but this was overcome by a new accelerator design allowing very high currents, 86 mA of H− and 37.3 mA of D−, to be extracted from a 16 mm diameter aperture.

The production of highly excited hydrogen atoms in proton collisions with the inert gases, hydrogen and nitrogen has been investigated within the energy range 4-20 keV. Cross sections for the formation of atoms in states with principal quantum number, n, between 24 and 40 have been determined using the field ionisation technique and found to scale as n-3. A comparison with optical data for n

Studies of beam transport through the planned ORNL 25 MV folded tandem accelerator demonstrate efficient utilization of phase-space acceptance and t?e feasibility of injecting buched beams from the tandem accelerator into the Oak Ridge Isochronous Cyclotron (ORIC). Use of a 180° bending magnet in the terminal provides outstanding charge state selection and permits better control of the high-energy beam transport than has previously been possible in coventional tandem acceler ators. Time spreads introduced in bunched beams by the 180° magnet are kept within a 6° RF acceptance window at ORIC provided the beam has a crossover in the center of the 180° magnet. Ion masses from 12 to 240 amu, preinjection energies from 150 to 500 keV and terminal voltages from 7.5 to 25 MV were studied for dc beams and beams bunched by various modulation techniques.

Summary The planning, execution and preliminary results of a major Anglo-German explosion seismic project are presented in this, paper I of a series. This Lithospheric Seismic Profile in Britain (LISPB) was planned as a reversed 1000 km line between two major sea-shot points off Cape Wrath in Scotland and one in the English Channel; additional sea-shots and intermediate land-shots were fired to give reversed and overlapping crustal coverage (to 180–400 km distance) along the line. In all, 29 shots were fired and 60 mobile magnetic tape stations recorded three-components of ground‘motion. The resulting 14 crustal and three long-range profiles have observations at intervals of typically 2–4 km. Recordings have been digitized and four examples of filtered, computer-plotted record sections are presented to illustrate data quality. In a preliminary analysis, phase correlations are discussed and some models presented; the latter especially are more relevant to future interpretations than to geological or tectonic problems. However, significant variations in crustal thickness and in the nature of the crust-mantle transition do seem to occur beneath the British Isles.

Electron capture collisions between Xe+ ions and the inert gases, hydrogen and methane have been investigated within the energy range 2-20 keV. Cross sections for the formation of bound (1S0) and metastable (6s'00 or 2P12/6s) have been separately determined, the latter by a novel detection technique involving laser photoionisation via an autoionising level. The results are in accord with current theoretical predictions where available.

In order to explain why the magnetic directions of naturally and artificially deposited fine silts show deviations from the direction of the ambient field a theoretical model has been postulated of the process of deposition. The deviations have been explained satisfactorily on the assumption that the sediment consists of quasi-spherical, non-cohesive particles which roll into hollows in the existing bed. A model of this kind provides a theoretical basis for the quantitative study of certain sedimentological questions which may be applied to the study of such problems as the apparent anomalous resistance to erosion of very fine grained sediments, their mechanism of compaction and the determination of current direction and velocity. Since it does not depend on direct observation either visual or mechanical the magnetic method may be particularly fruitful for sediments of fine silt grade where such observation is very difficult.

A pulsed ion source capable of delivering 10‐mA proton bursts with durations of approximately 1 nsec is described. Critical design constraints are discussed and used to illustrate the general procedure for meeting various experimental requirements. The system consists of a Duo‐Plasmatron ion source, a lens‐chopper combination, and a klystron buncher which uses the entire accelerator as a drift path to produce bunched ion bursts at the target. The equipment has been fitted into the terminal of the ORNL 3‐MV Van de Graaff accelerator. Since no accessory bunching magnets are used, ion bursts can be delivered to many different target stations. An external diverter system is used to vary the repetition rate from 106 sec−1 down to 3×104 sec−1.

Summary. Sediment of fine silt grade (10μm median diameter) has been deposited in a flume on beds of various small slopes. The deviation of the remanence due to the slope (the “bedding error”β) has been measured and its variation with the angle of slope α has been ascertained for a geomagnetic field inclination of 80°. The ratio β/α is compared with that observed by Rees (1964) in natural sediments, and with that predicted from a simple theoretical model. The observed and predicted results are in satisfactory agreement for both natural and artificial sediments.

Summary Experiments are described in which samples of unconsolidated glacial deposits from Sweden were redispersed and allowed to settle in a tank. The direction and intensity of the resultant magnetic field were varied and currents were created in the tank in an attempt to discover what factors, other than the magnetic field, control the alignment of the permanently magnetized particles which give the sediment its remanent magnetic moment. Two such factors were found to be important, namely the slope of the surface on which the sediment was deposited and the velocity of the current immediately above this surface. A tentative theory of the effect of slope is put forward which accounts almost quantitatively for the experimental results and in addition leads to a qualitative explanation of the effect of bottom currents. The relationship of these results to measurements of the direction of the natural remanence of the same material is discussed.

The method of measuring magnetic anisotropy in terms of the couple acting on a sample suspended in a magnetic field is well known. In recent years it has been used by Granar and by Stacey, among others, to determine what may be called the ‘magnetic fabric’ of rocks. In this paper two variations on Granar's magnetometer are described, designed respectively for (i) maximum sensitivity (minimum detectable susceptibility difference 10−10 emu/cm3) at fields of 20 oersteds or less and (ii) maximum convenience of operation at intermediate fields of 10 to 80 oersteds. An assessment is made of the importance of the various sources of error in measurement with the second instrument, and these experimental errors are compared with the natural scatter of principal axes of susceptibility of rock specimens.

Evaluations of various sources for accelerator use at proton currents above 10 ma indicate that a variation of Von Ardenne's Duo Plasmatron will give performance superior to that of any other source presently available. Operating characteristics for various sizes of the source have been examined for H1+, H2+, H3+, H1−, He+, and He++ ions and electrons. Experience with protons in the current range from 1 to 30 ma indicates that the Duo Plasmatron can deliver up to 100 amp/cm2 of exit aperture area. Current densities such as this cannot be maintained in the accelerator‐extractor section because of space charge forces, even at the highest gradients normally available for well‐polished electrodes in vacuum; thus it can be said that proton current densities will be space‐charge‐limited by the accelerator rather than emission‐limited by the source. Operation for He+ ions and electrons is similar to proton operation. Currents of 11 μa of H1− ions and 5 μa of He++ ions were extracted directly from a source which had been designed for a proton current of several milliamperes. The most striking features of the Duo Plasmatron are its remarkably high brilliance, high gas efficiency, good power economy, and compactness.

This paper describes a study of the shear strength S, the indentation hardness or yield pressure P and the coefficient of friction μ of polythene, P.T.F.E., Kel-F and Perspex over a temperature range from -100°C up to +80°C. In contrast to metals, the plastics show large changes in their strength properties over the temperature range used, and the confusing effect of surface films on the friction has been eliminated. According to the adhesion theory of friction μ is approximately equal to S/P. In these experiments it is found that μ varies closely with the ratio S/P, but the quantitative agreement is good only with polythene. With Perspex and Kel-F the observed values of μ are consistently larger than S/P, while with P.T.F.E. the values of μ are considerably lower. It is concluded that the adhesion theory can explain the friction behaviour of the plastics examined, the apparent discrepancies being due to the enhanced strength of the junctions under the high localized pressures existing at the interface (Perspex and Kel-F) or to structural factors which give a low intrinsic adhesion at the sliding interface (P.T.F.E.).

(Short communication) I. Introduction This work is part of a general programme of research being undertaken at Birmingham on the magnetic fabric of Lower Palaeozoic rocks. The method used of estimating palaeocurrents and other stresses is reviewed by Khan and Rees (1968). The outcrop of the Coniston Grit is shown on the Geological Survey Old Series Sheet No. 98. The grit consists of about a thousand metres of a rhythmic alternation of greywackes and subsidiary mudstones of turbidite facies (Furness et al., 1967). It passes downward into the Coniston Flags and upward into the Bannisdale Slates. These rocks were severely folded during the Caledonian orogeny: dips reach the vertical in many places and beds are locally overturned. Cleavage is strongly developed in the mudstones, usually as fracture cleavage, but true flow cleavage is occasionally to be seen in the fine-grained bands. The more massive greywackes, however, show little trace of strain and are not affected by cleavage. The intention of the survey was to define a set of near-contemporaneous palaeocurrent directions; and the mapped top of the Coniston Grit was taken as a collecting horizon for this purpose. As this boundary is transitional in character the contemporaneity is probably not very precise, and a further complication is introduced by the folding on a scale smaller than that mapped. Collecting was therefore confined to the north-western limbs of the north-east-trending synclines in an attempt to deal with only one tectonic situation. Dips at the seventeen localities from which forty-two oriented samples ...

An experimental study has been made of the friction and strength properties of crystalline materials such as rock-salt, lead sulphide and ice. From frictional measurements on rocksalt and from estimates of the real area of contact during sliding, the specific shear strength of the material at the rubbing interface is calculated and found to be nearly seven times as great as the bulk shear strength of a rock-salt single crystal. It is suggested that this is because the material in the region of contact is under very high hydrostatic pressures. Independent compression experiments of rock-salt crystals confirm this. Under high hydrostatic pressures brittle fracture is prevented, marked plastic deformation occurs and the plastic yield-stress reaches values very much greater than the bulk shear strength of an uncompressed specimen. As with metals, the plastic yield stress of rock-salt may be correlated with its indentation hardness. Experiments also show that if two rock-salt specimens are pressed together between rigid anvils so that there is appreciable plastic flow, very marked adhesion occurs between the crystals and the interface is almost as strong as a single crystal. In addition, hardness measurements of the track formed during sliding show that although there is some cracking and surface fragmentation the behaviour is dominated by plastic deformation of the surface layers. These results, and similar ones obtained with other brittle materials, suggest that the frictional behaviour of brittle solids is primarily due, as with metals, to local plastic flow and to strong interfacial adhesion at the regions of real contact.

By examining what is believed to be the physical basis of detrital remanent magnetism (DRM) we can set limits to the conditions under which it can occur. For example, detrital magnetism is not likely to be important in a sediment whose magnetic particles are less than 0.1 μ or greater than 50 μ or so in diameter. We can also set in order of importance the forces active in magnetization, and this leads to the conclusion that gravity is generally dominant at the instant of deposition. Both theories of DRM depend on this and are shown to be variants of the same basic theory. Future work should be directed toward the development of an improved form of this theory.

Measurements have been made to determine the seismic structure along the eastern branch of the East African Rift System.

This paper presents some data and results from a seismic refraction experiment, completed mainly in 1979 in the Rhenish Massif, Federal Republic of Germany and extending through Luxembourg and Belgium into the Paris Basin in France. Velocity-depth functions have been derived for each record section independently, based on the assumption that velocity varies only with depth: these models are being improved upon by time-term and ray-tracing methods capable of handling laterally varying velocity structures and by calculating synthetic seismograms. The Pg phase which is observed very clearly on all record sections represents a refracted wave, with velocity generally > 6 km/s, from depths below 1.5–5.5 km. Along the 600 km long main profile one intracrustal reflection can usually be recognized, while from the three shorter crossing profiles in the massif two intracrustal reflectors can always be seen. Beneath much of the main profile the crust-mantle boundary is either a first order discontinuity or thin (< 1 km) transition zone at ~30 km depth. However, beneath the Ardennes and West Eifel there is a 6–12 km thick transition zone before a velocity of 8.1 km/s is reached at ~36 km depth. Beneath the crossing profiles, there is generally a transition zone < 3 km thick between crust and mantle. In some cases, there can be recognized at the top of the mantle a thin high velocity layer which is underlain by a low velocity layer which, in turn, is underlain by a reflector 4–11 km below the crust-mantle boundary.

The importance of ferrihaem aggregation in studies of haemoglobin catabolism is assessed in the light of recent work. Experimental evidence is put forward suggesting that monomeric ferrihaems are degraded much more readily than dimeric species. This may offer an alternative explanation for the apparent `apoprotein catalysis' recently observed.