Dense Head Research Articles

Optimized voxel transformer for 3D detection with spatial-semantic feature aggregation

In this paper, we propose a novel 3D object detection model that leverages the advantages of the Voxel Transformer (VoTr) and the Confident IoU-Aware Single-Stage Object Detector (CIA-SSD) to address the challenges of detecting objects in 3D point clouds. Our model adopts the VoTr as its backbone, which enables long-range interactions between voxels via a self-attention mechanism. This overcomes the limitations of conventional voxel-based 3D detectors, which struggle to capture sufficient contextual information due to their restricted receptive fields. Our model also integrates the sparse voxel module and the submanifold voxel module, which efficiently process empty and non-empty voxel positions, effectively handling the natural sparsity and abundance of non-empty voxels. Moreover, inspired by the CIA-SSD design, our model incorporates the Spatial-Semantic Feature Aggregation (SSFA) module, which allows for the adaptive fusion of high-level abstract semantic features and low-level spatial features, ensuring accurate predictions of bounding boxes and classification confidence. Furthermore, based on the IoU-aware confidence rectification module, which refines the alignment between confidence scores and localization accuracy, we devise an Optimized RPN (Region Proposal Network) Detection Head module as a dense head to further predict the IoU loss and improve the accuracy. In this paper, we combine two state-of-the-art techniques to provide a precise and efficient solution for 3D object detection in point clouds. We evaluate our model on the KITTI dataset1 and achieve 76.56 % accuracy in terms of AP3D (%) Hard.

Locating and Counting Heads in Crowds With a Depth Prior.

To simultaneously estimate the number of heads and locate heads with bounding boxes, we resort to detection-based crowd counting by leveraging RGB-D data and design a dual-path guided detection network (DPDNet). Specifically, to improve the performance of detection-based approaches for dense/tiny heads, we propose a density map guided detection module, which leverages density map to improve the head/non-head classification in detection network where the density implies the probability of a pixel being a head, and a depth-adaptive kernel that considers the variances in head sizes is also introduced to generate high-fidelity density map for more robust density map regression. In order to prevent dense heads from being filtered out during post-processing, we utilize such a density map for post-processing of head detection and propose a density map guided NMS strategy. Meanwhile, to improve the ability of detecting small heads, we also propose a depth-guided detection module to generate a dynamic dilated convolution to extract features of heads of different scales, and a depth-aware anchor is further designed for better initialization of anchor sizes in the detection framework. Then we use the bounding boxes whose sizes are generated with depth to train our DPDNet. Considering that existing RGB-D datasets are too small and not suitable for performance evaluation of data-driven based approaches, we collect two large-scale RGB-D crowd counting datasets, which comprise a synthetic dataset and a real-world dataset, respectively. Since the depth value at long-distance positions cannot be obtained in the real-world dataset, we further propose a depth completion method with meta learning, which fully utilizes the synthetic depth data to complete the depth value at long-distance positions. Extensive experiments on our proposed two RGB-D datasets and the MICC RGB-D counting dataset show that our method achieves the best performance for RGB-D crowd counting and localization. Further, our method can be easily extended to RGB image based crowd counting and achieves comparable or even better performance on the RGB datasets for both head counting and localization.

First source-to-sink monitoring shows dense head controls sediment flux and runout in turbidity currents.

Until recently, despite being one of the most important sediment transport phenomena on Earth, few direct measurements of turbidity currents existed. Consequently, their structure and evolution were poorly understood, particularly whether they are dense or dilute. Here, we analyze the largest number of turbidity currents monitored to date from source to sink. We show sediment transport and internal flow characteristic evolution as they runout. Observed frontal regions (heads) are fast (>1.5 m/s), thin (<10 m), dense (depth averaged concentrations up to 38%vol), strongly stratified, and dominated by grain-to-grain interactions, or slower (<1 m/s), dilute (<0.01%vol), and well mixed with turbulence supporting sediment. Between these end-members, a transitional flow head exists. Flow bodies are typically thick, slow, dilute, and well mixed. Flows with dense heads stretch and bulk up with dense heads transporting up to 1000 times more sediment than the dilute body. Dense heads can therefore control turbidity current sediment transport and runout into the deep sea.

Bulbostylis itremoensis (Abildgaardieae, Cyperaceae), a new sedge species from Madagascar

SummaryAn endemic species of Bulbostylis (Abildgaardieae, Cyperaceae) from Madagascar is described as new to science. Bulbostylis itremoensis is only known from two localities: the Itremo and Isalo massifs in the province of Fianarantsoa. The species can be recognised by its habit with numerous crowded culms, leaves and thick, soft roots with an outer mycorrhizal layer. Its culm is hairy, angular with about 10 rounded longitudinal ridges without conspicuous surface cells. The leaf sheaths are light brown to straw-coloured with numerous longitudinal nerves, densely short-hairy on the nerves but with numerous flexuose whitish hairs at their oblique orifices. Its inflorescence is a dense hemispherical head of c. 15 crowded spikelets with many erect or spreading involucral bracts. Its glumes are ovate, densely scabrid of which medium-reddish brown with a prominent 1 – 3-nerved green midrib ending below the obtuse apex or excurrent into a short mucro. This species is described, illustrated and compared to the other species of Bulbostylis that occur in the Itremo Massif Protected Area.

The effect of mineral fertilizers on productivity of the new spring barley variety ‘Znatny’ in the non-blackearth part of the Russian Federation

An increase in spring barley acreage requires a detailed study of the interaction of agronomic and climatic factors, as well as the selection of a modern set of new varieties. The use of mineral fertilizers is one of the most important methods to improve the productivity of grain crops and maintain a deficit-free balance of mineral nutrients in arable soils. The current study of the effective use of various doses of mineral fertilizers (NPK) on the new spring barley variety ‘Znatny’ was carried out on dark-gray forest heavy loamy soil in 2018–2020 by the Institute of Seed production and Agrotechnologies, a branch of the Federal Budgetary Scientific Institution “Federal Research Agro-Engineering Center VIM”. There has been established that the date of the phenological phases and the length of interphase periods did not depend on fertilizer rates, but had a close correlation with weather conditions (r = +0.68). The analysis of the obtained data has shown that an increase in the rates of applied fertilizers increases the aboveground biomass, which, in turn, negatively affects productivity of the barley variety ‘Znatny’ (r = -0.77). The analysis of the yield structure and rates of fertilizers NPK has shown that in the trial, the spring barley productivity was influenced by 1000-grain weight (r = +0.60). There was found a high inverse correlation between productivity and length of head (r = -0.85). When length of head ranged from 7.5 to 8.4 cm, grain weight per head remained practically at the same level in all variants (1.1–1.2). This indicated that at a rate of N90P90K90 and N120P120K120, the variety ‘Znatny’ formed a not very dense head. Protein percentage at these rates also greatly reduced. According to the obtained data, an increase in the doses of applied fertilizers (N90Р90К90–N120Р120К120) resulted in the intensified development of most leaf diseases and a decrease in lodging resistance. Thus, the optimal dose of application of azophoska fertilizer on dark-gray forest soil is the norm N45P45K45, since on this option there was obtained maximum productivity and net income. the increase in the recom[1]mended norms of mineral fertilizers, sharply reduces profitability of crop cultivation.

Meteoroid Mass Estimation Based on Single‐Frequency Radar Cross Section Measurements

AbstractBoth high‐power large aperture radars and smaller meteor radars readily observe the dense head plasma produced as a meteoroid ablates. However, determining the mass of such meteors based on the information returned by the radar is challenging. We present a new method for deriving meteor masses from single‐frequency radar measurements, using a physics‐based plasma model and finite‐difference time‐domain (FDTD) simulations. The head plasma model derived in Dimant and Oppenheim (2017), https://doi.org/10.1002/2017ja023963 depends on the meteoroids altitude, speed, and size. We use FDTD simulations of a radar pulse interacting with such head plasmas to determine the radar cross section (RCS) that a radar system would observe for a meteor with a given set of physical properties. By performing simulations over the observed parameter space, we construct tables relating meteor size, velocity, and altitude to RCS. We then use these tables to map a set of observations from the MAARSY radar (53.5 MHz) to fully defined plasma distributions, from which masses are calculated. To validate these results, we repeat the analysis using observations of the same meteors by the EISCAT radar (929 MHz). The resulting masses are strongly linearly correlated; however, the masses derived from EISCAT measurements are on average 1.33 times larger than those derived from MAARSY measurements. Since this method does not require dual‐frequency measurements for mass determination, only validation, it can be applied in the future to observations made by many single‐frequency radar systems.

Hybrid event beds generated by erosional bulking of modern hyperpycnal flows on the Choshui River delta front, Taiwan Strait

AbstractHyperpycnal flows are important agents for transporting detrital sediments from rivers to oceans. Previous studies often assumed that the deposits of flood‐controlled delta fronts would be dominated by graded sand with common hummocky cross‐stratification. This study documents, for the first time, hybrid event beds and plumite deposits inside the succession of a modern delta front. This delta in the Taiwan Strait is fed by the Choshui River, which is considered a highly efficient sediment transport system with individual floods with extremely high suspended sediment concentrations. The deltaic event beds recorded in the core were interpreted as hyperpycnal flow‐generated hybrid event beds and turbidites triggered by hypopycnal flows. Accelerator Mass Spectrometry 14C dating, grain‐size analysis and measurements of stable isotopic composition of organic matter were conducted to delineate the depositional process of the recognized beds. The internal subdivisions of the hybrid event beds were differentiated mainly based on sedimentary textures, including cohesive mud content, sand content and sorting. The disorganized portion (division H3) appears internally chaotic and contains large rafted substrate clasts but also displays an upward increase in dispersed cohesive mud from 35% (division H3a) to 50% (division H3b). In contrast, massive H1 divisions are characterized by much lower cohesive mud of ca 8%. The vertical arrangement between depositional facies allows the discrimination of three hybrid event bed types. The stable carbon isotopic composition of the organic matter reveals that the cohesive mud in each division of the hybrid event beds was sourced from marine substrate, rather than supplied by the original hyperpycnal flows. Therefore, the hybrid event beds are generated by energetic hyperpycnal flows, which can delaminate the muddy sea‐floor and incorporate large quantities of substrate fragments. The bulking of erosional hyperpycnal turbulent flow forces flow transformation and generates a more cohesive flow with a turbulent, dense head and trailing bipartite debris flow. The occurrence of hybrid event beds in modern shallow delta front settings is also an important novelty, implying a high density of hyperpycnal flows at the mouth of sediment‐laden rivers as well as the crucial impact of substrate entrainment on the development of hybrid event beds.

Perceptual implications of different Ambisonics-based methods for binaural reverberation.

Reverberation is essential for the realistic auralisation of enclosed spaces. However, it can be computationally expensive to render with high fidelity and, in practice, simplified models are typically used to lower costs while preserving perceived quality. Ambisonics-based methods may be employed to this purpose as they allow us to render a reverberant sound field more efficiently by limiting its spatial resolution. The present study explores the perceptual impact of two simplifications of Ambisonics-based binaural reverberation that aim to improve efficiency. First, a "hybrid Ambisonics" approach is proposed in which the direct sound path is generated by convolution with a spatially dense head related impulse response set, separately from reverberation. Second, the reverberant virtual loudspeaker method (RVL) is presented as a computationally efficient approach to dynamically render binaural reverberation for multiple sources with the potential limitation of inaccurately simulating listener's head rotations. Numerical and perceptual evaluations suggest that the perceived quality of hybrid Ambisonics auralisations of two measured rooms ceased to improve beyond the third order, which is a lower threshold than what was found by previous studies in which the direct sound path was not processed separately. Additionally, RVL is shown to produce auralisations with comparable perceived quality to Ambisonics renderings.

Determination of Selected Heavy Metals Content and Health Risk Assessment of Cabbage Cultivated in Elalla Farmland, Mekelle, Ethiopia

Like other countries in Ethiopia vegetables are vital edible plants which are a crucial part of the human food. One from these vegetables cabbage is a leafy green biennial plant grown as an annual vegetable for its dense leaved heads. The heavy metal content of cabbage may vary on the composition of the water and nature of soil. The study was aimed to determine concentration of selected heavy metals like Cadmium (Cd), Chromium (Cr), Cupper (Cu), Lead (Pb), Iron (Fe) and Zinc (Zn) were measured in edible portion of cabbage and soils around four sites of cabbage production area in Elalla farmland Mekelle, Tigray, Ethiopia , and the potential health risk of heavy metal contamination to the local population via vegetable consumption, Transfer factor and daily intake of metal was also evaluated. The level of heavy metals in soil and Cabbage vegetable were determined by flame atomic absorption spectrophotometer (FAAS) that uses acetylene as fuel with air. The concentration of Cd (17.15 ± 1.26 to 17.52 ± 0.24) mg/Kg and Zn (325.10 ± 6.00 to 512.86 ± 3.13) mg/Kg in the soil sample exceeds from the limit the guideline of agricultural soil and the mean concentrations of Fe, Cu, Pb and Cr is below the guideline of agricultural soil. The mean concentration of Pb(3.060 ± 0.18 to 5.982 ± 0.11), Zn(144.662 ± 3.16 to 173.660 ± 2.18), Cr(11.825 ± 0.18 to 13.482 ± 0.37) and Cd(0.309 ± 0.01 - 0.712 ± 0.06) in all study sites of cabbage samples were exceeded the permissible limits set by FAO but Pb and Fe are below the permissible limit. The TF calculated were also investigated lower for all metals and for the value of HRI is below 1, according to the present study the result indicates that exposed population is assumed to be safe. As the results show that HRI of contamination in cabbage has less health risk to the consumers. Keywords: - Cabbage, Heavy metals, Health Risk, Health Risk Assessment, Daily Intake Metal DOI : 10.7176/CMR/11-6-03 Publication date : August 31st 2019

MUD, the next generation in acoustic backscatter sediment measurements

Detection and classification of sediments within rarely occurring turbidity flows is challenging, in part because of the acoustic absorption and scattering within the dense suspended sediments. A new calibrated acoustic backscatter echosounder, the Multifrequency Ultrasonic Device (MUD™), was deployed from 13 to 16, May 2018, at about 120 m water depth within Bute Inlet, Canada. The MUD prototype (1.2 MHz, 769 kHz and 200 kHz) was deployed in a tautline mooring which included a passive acoustic recorder, an ADCP, CT sensor and OBS sensor. The frequencies for the prototype were selected to allow for a compromise between good acoustic range and penetration into dense flows with the potential for particle size discrimination. Preliminary analysis of the data indicates the presence of three turbidity flows over a two-hour period with speeds of up to 2.5 m/s. As anticipated, the lower frequencies did better in penetrating through the dense turbidity flow. This suggests that it will be possible to use inversion of the acoustic backscatter to estimate sediment concentrations within the dense head of the turbidity flow. Multifrequency inversion techniques will be applied to the less dense portion of the flow to estimate particle size distributions. Detection and classification of sediments within rarely occurring turbidity flows is challenging, in part because of the acoustic absorption and scattering within the dense suspended sediments. A new calibrated acoustic backscatter echosounder, the Multifrequency Ultrasonic Device (MUD™), was deployed from 13 to 16, May 2018, at about 120 m water depth within Bute Inlet, Canada. The MUD prototype (1.2 MHz, 769 kHz and 200 kHz) was deployed in a tautline mooring which included a passive acoustic recorder, an ADCP, CT sensor and OBS sensor. The frequencies for the prototype were selected to allow for a compromise between good acoustic range and penetration into dense flows with the potential for particle size discrimination. Preliminary analysis of the data indicates the presence of three turbidity flows over a two-hour period with speeds of up to 2.5 m/s. As anticipated, the lower frequencies did better in penetrating through the dense turbidity flow. This suggests that it will be possible to use inversio...

Front propagation of gravity currents on inclined bottoms in linearly stratified fluids

Gravity currents propagating on an inclined bottom into stratified environment can be frequently encountered in nature or engineering fields. However, theoretical analysis and simulations on the evolution process of lock-exchange gravity currents in such environments are still in lack of investigations. In this work, we derive a set of semi-empirical formulae to determine the frontal propagation speed in homogenous and linearly stratified ambient fluids. Two phases can be clearly observed in the propagation process, a relatively short acceleration phase followed by a deceleration phase. In the acceleration phase, the formula considers the influence of initial position and ambient stratification by introducing mass centroid coefficient (αp) and effective stratification coefficient (αs), respectively. In the deceleration phase, the formula is derived by adding the effective buoyancy parameter Bm′ and entrainment coefficient km, where km is eventually a function of the fraction of heavy fluid in the dense current head (χ) as it propagating down the ramp. We propose a simplified and efficient method to estimate the value of χ in various conditions, which has been previously assumed as a constant. A series of lock-exchange gravity current experiments were conducted in the tank with linear stratifications to validate the propagation theory. The comparisons between the calculated and measured front propagation speed show good agreement, which reveal that the front velocity exhibits a rapid acceleration stage followed by a deceleration stage in the linearly stratified ambience. The good agreement between measured and calculated data indicates that semi-empirical formulae are capable to predict the whole process of gravity current propagation using only measurable information prior to initiate gravity current experiments.

“Comets” orbiting a black hole

We use a long (300 ksec), continuous Suzaku X-ray observation of the active nucleus in NGC1365 to investigate the structure of the circumnuclear BLR clouds through their occultation of the X-ray source. The variations of the absorbing column density and of the covering factor indicate that the clouds surrounding the black hole are far from having a spherical geometry (as sometimes assumed), instead they have a strongly elongated and cometary shape, with a dense head (n=10^11 cm^-3) and an expanding, dissolving tail. We infer that the cometary tails must be longer than a few times 10^13 cm and their opening angle must be smaller than a few degrees. We suggest that the cometary shape may be a common feature of BLR clouds in general, but which has been difficult to recognize observationally so far. The cometary shape may originate from shocks and hydrodynamical instabilities generated by the supersonic motion of the BLR clouds into the intracloud medium. As a consequence of the mass loss into their tail, we infer that the BLR clouds probably have a lifetime of only a few months, implying that they must be continuously replenished. We also find a large, puzzling discrepancy (two orders of magnitude) between the mass of the BLR inferred from the properties of the absorbing clouds and the mass of the BLR inferred from photoionization models; we discuss the possible solutions to this discrepancy.

The Star Formation in the L1615/L1616 Cometary Cloud

The present work aims at performing a comprehensive census and characterization of the pre-main-sequence (PMS) population in the cometary cloud L1615/L1616, in order to assess the significance of the triggered star formation scenario and investigate the impact of massive stars on its star formation history and mass spectrum. Our study is based on UBVRCIC and JHKs photometry, as well as optical multiobject spectroscopy. We performed a physical parameterization of the young stellar population in L1615/L1616. We identified 25 new T Tauri stars mainly projected on the dense head of the cometary cloud, almost doubling the current number of known members. We studied the spatial distribution of the cloud members as a function of the age and Hα emission. The star formation efficiency (SFE) in the cloud is ~7%-8%, as expected for molecular clouds in the vicinity of OB associations. The slope of the initial mass function (IMF), in the mass range 0.1 M☉ ⩽ M ⩽ 5.5 M☉, is consistent with that of other T and OB associations, providing further support of a universal IMF down to the hydrogen-burning limit, regardless of environmental conditions. The cometary appearance, as well as the high SFE, can be explained in terms of triggered star formation induced by the strong UV radiation from OB stars or supernova shock waves. The age spread and both the spatial and age distribution of the PMS objects provide strong evidence of sequential, multiple events and possibly still ongoing star formation activity in the cloud.

Genotypic and environmental effects on selenium concentration of broccoli heads grown without supplemental selenium fertilizer

AbstractSelenium (Se) is an important trace element in human nutrition that is essential to normal health. Broccoli is known to accumulate relatively high concentrations of Se, and there is strong evidence that consumption of Se‐enriched broccoli florets decreases cancer risk. In light of the above, this study was conducted to evaluate differences in Se concentration per head and total Se head content for a collection of broccoli hybrids (20) and inbreds (15) grown in field environments without supplemental Se fertilization. Our objectives were to assess the relative importance of genotype vs. environment in affecting Se levels and to determine if Se content is associated with other important horticultural traits. When analysed over three environments, there was a significant genotype effect for Se head concentration with hybrids, but not inbreds, but the environmental effect was about 10 times larger than that for genotype. Total Se content (ng/head) varied significantly among hybrids and inbreds, but as with concentration, environmental effects were also much larger for this trait. Head Se concentrations for hybrids ranged from 52.7 to 84.7 ng/g and total Se accumulation ranged from 563 to 885 ng/head. The same respective traits ranged from 49.3 to 80.0 ng/g and 678 to 876 ng/head for inbreds. There was no correlation between Se head concentration and head dry mass or days from transplant to maturity for either hybrids or inbreds. There was no evidence that Se might be diluted in broccoli heads as mass increases with cultivars that produce dense heads. Results indicate that it should be feasible to combine relatively high Se concentration or content with high head dry matter (DM), a phenotype that broccoli breeders might strive to achieve.

The role of dynamic recrystallization in [001] single-crystal W and W-Ta alloy ballistic rod penetration into steel targets

The microstructures of long rod [001] single-crystal penetrators of W grown by CVD and zone melt processing, and W-5% Ta grown by zone melt (ZM) processing, were examined before and after penetration into RHA steel targets, by optical metallography and transmission electron microscopy. The initial Vickers microhardness values for the CVD-W rods was 417 VHN in contrast to 485 VHN for the ZM-W and W-5% Ta rods as a consequence of an order of magnitude larger dislocation density. Both the CVD-W and ZM-W exhibited less dense head flow associated with adiabatic shear bands and dynamic recrystallization (DRX) than the ZM-W-5% Ta, but all penetrators exhibited erosion tube formation in the penetration channel. These tube and erosion debris particles exhibited dense, overlapping shear bands composed of DRX grains or areas with larger, equiaxed grains resulting from residual grain growth. These observations suggest that controlling the penetrator head flow by solute-induced DRX may control penetration.

Genetic and environmental effects on glucosinolate content and chemoprotective potency of broccoli

AbstractBroccoli is well recognized as a source of glucosinolates and their isothiocyanate breakdown products. Glucoraphanin is one of the most abundant glucosinolates present in broccoli and its cognate isothiocyanate is sulphoraphane, a potent inducer of mammalian detoxication (phase 2) enzyme activity and anti‐cancer agent. This study was designed to measure: glucosinolate levels in broccoli florets from an array of genotypes grown in several environments; the elevation of a key phase 2 enzyme, quinone reductase, in mammalian cells exposed to floret extracts; and total broccoli head content. There were significant environmental and genotype‐by‐environment effects on levels of glucoraphanin and quinone reductase induction potential of broccoli heads; however, the effect of genotype was greater than that of environmental factors. The relative rankings among genotypes for glucoraphanin and quinone reductase induction potential changed, when expressed on a per head basis, rather than on a concentration basis. Correlations of trait means in one environment vs. means from a second were stronger for glucoraphanin and quinone reductase induction potential on a per head basis than on a fresh weight concentration basis. Results of this study indicate that development of a broccoli phenotype with a dense head and a high concentration of glucoraphanin to deliver maximum chemoprotective potential (high enzyme induction potential/glucoraphanin content) is a feasible goal.

Grain Growth in the Dark Cloud L1251

We have performed optical imaging observations of the dark cloud L1251 at multiple wavelengths, B, V, R, and I, using the 105 cm Schmidt telescope at the Kiso Observatory, Japan. The cloud has a cometary shape with a dense showing star formation activity and a relatively diffuse without any signs of star formation. We derived extinction maps of A_B and A_V with a star count method, and also revealed the color excess (E_{B-V}, E_{V-R}, and E_{V-I}) distributions. On the basis of the color excess measurements we derived the distribution of the ratio of total to selective extinction R_V over the cloud using an empirical relation between R_V and A_lambda/A_V reported by Cardelli et al. In the tail of the cloud, R_V has a uniform value of ~3.2, close to that often found in the diffuse interstellar medium (~3.1), while higher values of R_V=4-6 are found in the dense head. Since R_V is closely related to the size of dust grains, the high R_V-values are most likely to represent the growth of dust grains in the dense star-forming head of the cloud.

Eucommiitheca hirsuta, a new pollen organ withEucommiiditespollen from the Early Cretaceous of Portugal

Abstract A new pollen organ, Eucommiitheca hirsuta, containing Eucommiidites pollen grains is described from the Early Cretaceous of Portugal. The material comprises dispersed microsporangiate units and fragments of axes bearing microsporangiate units in an opposite and decussate arrangement. Each microsporangiate unit consists of a slightly angular to rounded peltate scale attached centrally to a short stalk, and with whorls of sporangia around the distal part of the stalk. Sporangia are stalked and free, with longitudinal dehiscence, and contain pollen grains similar to the characteristic dispersed pollen genus Eucommiidites. Eucommiitheca is comparable to Erdtmanitheca, another Cretaceous pollen organ containing Eucommiidites pollen, in the peltate nature of the microsporangiate units, but microsporangiate units in Erdtmanitheca are arranged in dense heads and sporangia are elongate. The opposite and decussate arrangement of the microsporangiate units in Eucommiitheca is in accordance with the possible...

Environmental factors influencing head density and diameter of crisp lettuce cv. Saladin

Crops of the crisp lettuce cv. Saladin were grown in 1988 and 1989 on four sites with up to four transplantings each year. After hearting the weight and size of heads were recorded weekly throughout growth, enabling head density to be calculated. Head density reached a minimum value during the mid-period of head growth and then increased to the value recorded at maturity. Denser heads were associated with low temperatures during the period up to and around hearting while less dense heads were primarily associated with higher temperatures in the period up to hearting and high levels of solar radiation in periods well after hearting. Larger heads were associated with low temperatures up to and around hearting, with very high temperatures in the immediate post-hearting period and with large amplitudes of temperature change and high levels of solar radiation around hearting. Smaller heads were primarily associated with high temperatures before hearting. The results demonstrate the sensitivity of the lettuce crop to environmental variables at specific stages of growth and our analysis of them may provide some explanation of the variation in head density and size observed between crops.

The morphology of human immunodeficiency virus particles by negative staining electron microscopy.

Negative staining electron microscopy was used to examine culture fluids from the H9/HTLV-III cell line after concentration by centrifugation. Characteristic retrovirus-like particles bearing distinctive envelope projections were seen. The virion envelope was frequently extended in the form of a bleb or a tail. These particles were morphologically virtually indistinguishable from similar preparations of Friend murine leukaemia virus. H9/HTLV-III culture fluids contained, in addition, numerous comet-shaped particles with a dense head and flared tail. These particles were clumped by the addition of anti-HTLV-III-positive serum suggesting that they may represent intermediate forms of the virus.