Shield Length Research Articles

A new thylacocephalan crustacean from the Upper Jurassic lithographic limestones of southern Germany and the diversity of Thylacocephala

Thylacocephala is a group of extinct eucrustaceans of presumably predatory nature. We describe here a new genus and species of thylacocephalan crustaceans from the Upper Jurassic Solnhofen limestones of Eichstatt (Altmuhltal Formation), Falcatacaris bastelbergeri n. g. n. sp. (about 150 million years old). Falcatacaris bastelbergeri n. g. n. sp. is the fourth species of Thylacocephala found in these deposits. The species differs significantly from other thylacocephalans, especially by characters of the shield. The shield of the specimen is rather low (short in dorsoventral extent) and it bears a long rostrum but no elongated posterior spine. For comparative purposes, we provide an overview of the shield morphology of known thylacocephalan species from literature as well as a morphological analysis of the group. An elliptic Fourier analysis is used to compare the different shield shapes of thylacocephalans to each other; results are presented in PCA plots. Shield length and anterior or posterior shield extensions are the characters with the most variation in thylacocephalan shield morphology.

Simulation and Optimization of Temperature Field in Large-Sized MOCVD Reactor by Resistance Heating

The effect of the number of layers and the length of the heat shields on the heating efficiency and temperature distributions in the substrate have been studied by establishing the model of a single-piece 18-inch MOCVD reactor. The results show that the number of layers of the heat shields is directly proportional to the heating efficiency, decreasing the length of the thermal shield can reduce the standard deviation(STD) of the substrate temperature. When the length of the heat shields is 56mm, the coefficient of substrate temperature STD is 21.41 °C and the STD is about 45% lower than the traditional susceptor. An area within substrate radius of 200mm, the coefficient of substrate temperature STD is 2.64 °C and the STD is about 93% lower than the traditional susceptor. The results obtained will provide theoretical basis for developing the heating structure of large-sized MOCVD reactor.

The Population and Reproductive Characteristics of the Hermit Crab Pagurus brachiomastus (Thallwitz, 1892) (Decapoda: Paguridae) from Peter the Great Bay, the Sea of Japan

The population and reproductive characteristics of the hermit crab Pagurus brachiomastus (Thallwitz, 1892) have been examined in Vostok Bay (Peter the Great Bay, Sea of Japan). The average population density of P. brachiomastus was lowest in the spring (2.4 ± 0.6 ind./m2) and highest (3.1 ± 0.4 ind./m2) in the summer; the biomass was 18.24 ± 3.75 and 22.83 ± 2.80 g/m2, respectively. Hermit crabs were found throughout the depth range from 0 to 12 m, but were most numerous at a depth of approximately 5–6 m, with an average population density of 8.3 ± 3.7 ind./m2 and a biomass of 39.09 ± 8.51 g/m2 in the summer. The shield length of males varied from 1.3 to 10.3 mm (on average, 5.3 ± 2.2 mm), that of females varied from 1.3 to 10.6 mm (on average, 4.3 ± 1.5 mm), and that of ovigerous females varied from 1.5 to 8.4 mm (on average, 4.4 ± 1.5 mm). The male to female ratio varied from 0.8 to 3.3 during the observation period, with an average of 1.7. Spawning continued from March through August. The proportion of ovigerous females increased from 8.5% in March to 82.8% in May; embryos in clutches remained in the early stage of development until the second 10-day period of May. Egg development was resumed when the water temperature reached 10°C. Breeding was asynchronous: in June–August, females with late-stage embryos and females with recently laid eggs were observed, indicating the possibility of repeated spawning. The data we obtained showed that the favorable coexistence of P. brachiomastus with other sympatric species in the study area is provided by the spatial dissociation of their clusters and differences in size characteristics, as well as the presence of an embryonic diapause in egg development in part of the females and the possibility of repeated spawning.

Second world record of Olopachys hallidayi Özbek, 2014 (Mesostigmata: Pachylaelapidae) from Iran

The species Olopachys ( Olopachys ) hallidayi was collected from orchards from Maragheh and adjacent villages, East Azerbaijan Province, using Berlese-Tullgren funnel during the autumn 2016. The specimens were cleared in Nesbitt's fluid, then mounted on microscope slides using Hoyer's medium, and finally dried in an oven at 45–50 °C for 3–4 weeks. The Iranian specimens of Olopachys hallidayi are very similar to the Turkish ones according to the morphometric characteristics and the original description prepared by Ozbek (2014), but they have wide ranges for some characteristics. The Iranian specimens were larger than the Turkish ones in length and width of dorsal shield, although the ratio was smaller in the Iranian specimens [740−875 long, 480−580 wide, the ratio: 1.47−1.54 in the Iranian specimens; 700−780 long, 430−470 wide, the ratio: 1.54−1.69 in the Turkish specimens (Ozbek 2014)].

Sexual Dimorphism and Seasonal Variability of Shield Size in the Endangered Hawaiian Coot (Fulica alai)

The endangered Hawaiian Coot (Fulica alai) is one of few native waterbird species remaining in Hawaii, USA. On the island of Oahu, 56 adults were captured and sexed using a molecular method, and sexual dimorphism, seasonal variation in shield size (possibly sexually selected), and use of morphometrics to predict sex as an alternative to molecular sexing were investigated. The sex ratio was significantly male biased: 39 males, 17 females (P = 0.003). No morphometric character assessed independently differed significantly between sexes (0.056 < P < 0.975). However, a multiple regression approach indicated that tarsus length, bill height, tail length, and wing length in combination differed between sexes, but prediction of sex was nonetheless possible with only 65% accuracy. Male shield size was larger during the pre-breeding and breeding seasons than the post-breeding season, but did not vary significantly in females, the interaction between sex and season in the model being significant (P < 0.02). Within the breeding and pre-breeding seasons (a subsample of total birds), multiple regression indicated sexual dimorphism in shield width, shield length, and wing length, but prediction of sex was again only possible with 68% accuracy. Thus, neither model predicted sex sufficiently accurately for this morphometric approach to be a viable substitute for molecular sexing.

Population structure and morphology of South African deep‐water parapagurid hermit crabs

AbstractThe parapagurid hermit crabs Sympagurus dimorphus (Studer, 1883) and Parapagurus bouvieri (Stebbing, 1910) form dominant components of South African deeper‐water benthic invertebrate communities and, as adults, forego the use of “traditional” gastropod shells in favour of symbiotically associated Epizoanthus carcinoecia. A total of 1,122 adult S. dimorphus and 549 adult P. bouvieri derived from demersal research trawl surveys were examined to investigate parameters of population structure, carcinoecia association and morphology. S. dimorphus had a female‐biased sex ratio of 1:1.5, and P. bouvieri an equal sex ratio of 1:1. The proportion of males of both species increased with cephalothoracic shield length (CL). The lengths of the major right chelipeds of both S. dimorphus males and females, and P. bouvieri males were positively allometric, and negatively allometric in P. bouvieri females. All P. bouvieri inhabited carcinoecia, while 3.39% (n = 38) of S. dimorphus specimens occupied gastropod shells. There was a positive relationship between S. dimorphus CL and rate of gastropod shell occupation (r2 = 0.96). In S. dimorphus, number of zoanthid polyps forming the carcinoecia pseudoshell increased with both total shell volume (R2 = 0.73) and colony height (R2 = 0.61), but no such relationships were found for P. bouvieri. Euspira napus was the most common original shell around which carcinoecia developed in both S. dimorphus (45.45%) and P. bouvieri (39.00%). We speculate that these hermit species exist along an evolutionary continuum of carcinoecia use. Sympagurus dimorphus retains the ability to occupy both gastropod shells and pseudoshells and, like most other hermit crabs, continue to use shells/carcinoecia as shelters to protect the entire body. In contrast, adult P. bouvieri appear to be totally reliant on carcinoecia, which they use more as a brood pouch covering only the abdomen, rather than as a shelter into which they can fully retract to escape predation.

QED plasma in the early universe

Renormalization scheme of quantum electrodynamics (QED) at high temperatures is used to calculate the effective parameters of relativistic plasma in the early universe. Renormalization constants of QED play the role of effective parameters of the theory and can be used to determine the collective behavior of the medium. We explicitly show that the dielectric constant, magnetic reluctivity, Debye length and the plasma frequency depend on temperature in the early universe. Propagation speed (v_{prop}), refractive index (i_r), plasma frequency (omega ) and Debye shielding length (lambda _D) of a QED plasma are computed at extremely high temperatures in the early universe. We also found the favorable conditions for the existence of relativistic plasma from these calculations.

Low-temperature tolerance of early juveniles of six terrestrial hermit crab species

Abstract Because temperature strongly influences biological processes of ectotherms, it also plays a fundamental role in determining their geographical distribution. We evaluated the low-temperature tolerance of early juveniles of six terrestrial hermit crab species in the family Coenobitidae (genera Birgus and Coenobita), B. latro, C. brevimanus, C. cavipes, C. purpureus, C. rugosus, and C. violascens that occur in the northwestern Pacific region, Japan. A total of 30 laboratory-raised juveniles (about 1 mm in shield length) carrying gastropod shells were individually stocked in small plastic cups with sandy bottoms in temperature-controlled incubatory chambers at ∼27°C. The temperature was reduced by 1°C every 48 h, and the juveniles were observed until all the crabs had died; the median lethal temperature (MLT) was estimated as the temperature at which 50% of the test juveniles had died. The MLT estimates varied significantly among the species, and the most northward distributed species, C. purpureus, had the lowest MLT values. The phylogeny, paleoceanography, paleogeography, and paleoclimatology suggest that cooler thermal regimes might have acted as an evolutionary force for the divergence of C. purpureus in the Pliocene. A negative correlation was found between the northern latitudinal limit of distribution and the MLT values, even after controlling for the phylogenetic relationships in the six coenobitids. A temperature-dependent biogeography was thus recognized in terrestrial hermit crab species in the northwestern Pacific region, and global warming is expected to affect their geographical distributions.

Geographical variation in fecundity and reproductive investment of Loxopagurus loxochelis (Decapoda: Anomura: Diogenidae) along the south-eastern coast of Brazil

ABSTRACTWe aimed to study the fecundity and reproductive investment of Loxopagurus loxochelis under different environmental conditions. In total, 67 ovigerous females were analyzed, 20 from Macaé, 26 from Ubatuba and 21 from Cananéia. The cephalothoracic shield length, fecundity and reproductive investment (Ubatuba 10.2%, Macaé 8.9% and Cananéia 7.5%) were different among the regions (ANCOVA, p < 0.05), caused by different abiotic resources and environmental characteristics found in each sampling region. Cananéia had the smallest individuals and low availability of adequate shells to hermit crabs, a condition that may have affected the growth and reproduction of the animals. Macaé has a continuous transport of nutrients such as nitrogen and phosphorus to the surface promoted by the Cabo Frio Upwelling zone, which may be a favourable condition for plankton production and, consequently, the extended ‘match/mismatch’ adjustment of spawning females of L. loxochelis. We propose that the highest reproductive investment on the Ubatuba coast is a consequence of regional environmental scenarios of waters colder than the Cananéia region, i.e. females concentrate more energy to reproduce seasonally. Thus, we proved that patterns of L. loxochelis’ reproduction can change on a regional scale according to the local condition of shell supply and water temperature.

Morphometric analysis in different geographical populations of Varroa destructor (Acari: Varroidae) associated with Apis mellifera colonies in Iran

Varroa destructor is a major ectoparasitic mite which feeds on the western honey bee, Apis mellifera hemolymph. Morphometric analysis of V. destructor in Iran was performed in order to detect differences within some populations of the species. Totally, 145 female mites were collected from A. mellifera colonies in different geographical regions in Iran and Europe (Spain and France). Eight morphological variables were measured: 1) length of dorsal shield (LDS), 2) width of dorsal shield (WDS), 3) length of genital shield (LGS), 4) width of genital shield (WGS), 5) length of metapodal shield (LMS), 6) width of metapodal shield (WMS), 7) length of anal shield (LAS) and 8) width of the anal shield (WAS). The ratios of LDS/WDS, WDS/LDS, LGS/WGS and LAS/WAS were also calculated. Multivariate analyses demonstrated significant differences in means of body length (LDS) and body width (WDS) between populations. Using principal component analysis (PCA) and cluster analysis with pair group method, five morphological groups were established. PCA analyses were also shown one morphotype, A3, between samples. Collectively, our findings suggest a wide phenotypic plasticity within the populations of Varroa mite in Iran.

Population biology and reproductive characteristics of the hermit crab Pagurus minutus Hess, 1865 (Decapoda: Anomura: Paguridae) in the northern part of the species range (Peter the Great Bay, the Sea of Japan)

ABSTRACTPopulation and reproductive characteristics of the hermit crab Pagurus minutus Hess, 1865 were examined in the northern part of the species range (Vostok Bay, Peter the Great Bay, the Sea of Japan). The average population density was 13 ± 4 SE ind/m2 and did not change during the year; the average biomass was 12.56 ± 3.43 SE g/m2. Hermit crabs were found at a depth of 0–6 m, but were most numerous at 0–1 m in summer and at 2–3 m in winter, hence this species showed distinct seasonal migrations. The shield length of males varied from 1.0 to 7.0 mm and females from 1.1 to 4.7 mm. The population of P. minutus was significantly female-biased. Females attained sexual maturity at a shield length of more than 1.1 mm. Ovigerous females were found from early May to early September. Pagurus minutus has no embryonic diapause, with the incubation period lasting about a month. The increase in the number of females with eggs at early developmental stages in July–August suggested that repeated ovipositions took place in summer. The prevalence of females in the population and their early maturation, multiple spawning, the release of larvae during the most favourable time for their development, and distinct vertical migrations allowing avoidance of the negative effect of the ice-cover, ensure high abundance of P. minutus in the northern part of the species range.

Morphometric identification of Varroa destructor and its plasticity by the exposure to thymol

Actualmente existen cuatro especies de Varroa identificadas en todo el mundo, las cuales presentan una alta variabilidad interespecifica e intraespecifica. El objetivo de esta investigacion fue identificar la especie predominante de Varroa y el efecto del timol sobre la plasticidad del acaro. Para determinar la especie y el efecto del timol sobre la plasticidad del acaro se analizaron morfometricamente 150 especimenes de 65 colmenas y 54 de 17 colmenas expuestas a timol por 28 dias. De acuerdo a las medidas morfometricas, los acaros fueron identificados como Varroa destructor, no habiendo evidencia morfometrica de la infestacion por otras especies del genero Varroa. Las poblaciones de acaros difieren entre apiarios (P≤ 0.05), por lo que las variables ancho del escudo genital (P=0.013), largo del escudo genital (P=0.002) y ancho del escudo anal (P=0.026) fueron mas variantes. Se encontraron 8 morfotipos, observandose diferencias entre las medias de largo del escudo genital por efecto del timol (P≤ 0.05). Se concluye que Varroa destructor expuesta al timol presenta una variabilidad morfometrica intraespecifica por la adaptacion a la presion de seleccion impuesta por el acaricida.

Method for reducing measurement errors of a Langmuir probe with a protective RF shield

Probe measurements were conducted in the middle cross-section of an inductive, low-pressure xenon plasma using a straight cylindrical Langmuir probe with a bare metal shield that protected the probe from radio frequency interference. As a result, reliable radial distributions of the plasma parameters were obtained. Subsequent analyses of these measurements revealed that the electron energy distribution function (EEDF) deviated substantially from the Maxwellian functions and that this deviation depended on the length of the probe shield. To evaluate the shield's influence on the measurement results, in addition to the probe (which was moved radially as its shield length varied in the range of lsh1 = lmax–0), an additional L-shaped probe was inserted at a different location. This probe was moved differently from the first probe and provided confirmational measurements in the common special position where lsh1 = 0 and lsh2 ≠ 0. In this position, the second shield decreased all the plasma parameters. A comparison of the probe datasets identified the principles of the relationships between measurement errors and EEDF distortions caused by the bare probe shields. This dependence was used to correct the measurements performed using the first probe by eliminating the influence of its shield. Physical analyses based on earlier studies showed that these peculiarities are caused by a short-circuited double-probe effect that occurs in bare metal probe protective shields.

The Screening Effect in a Fermi Plasma

The present work considers an electron gas where ion contributions to the static potential may be neglected. The influence of temperature on the static potential and also on the screening length are derived. In the present contribution the temperature issue for a Fermi gas is treated in its non-relativistic as well as relativistic form. The effect of an extraneous ion in a degenerate Fermi plasma is analysed and a temperature dependent electrostatic shielding length in a degenerate Fermi plasma is determined.

Supersonic flows past an obstacle in Yukawa liquids

Shock formation, when a supersonic flow passes a stationary obstacle, is ubiquitous in nature. Considering particles mediating via a Yukawa-type interaction as a prototype for a strongly coupled complex plasma, characterized by coupling strength (Γ, ratio of the average potential to kinetic energy per particle) and screening parameter (κ, ratio of the mean inter-particle distance to the shielding length), we address the fundamental problem of supersonic fluid flow U0, past a stationary obstacle immersed in this strongly coupled system. We here report the results on the bow shocks formed in Yukawa liquids when the liquid flows at speeds larger than the speed of sound in the system. Depending on the values of Mach number MCL=U0CL, where CL is the longitudinal speed of sound in the system, the bow shocks are found to be either traveling or localized. We find that for the transonic flows (0.8 ≲MCL≲ 1.2), the bow shocks travel in the upstream direction opposite to the incoming fluid. The phase velocity of the traveling bow shocks is found to be a non-monotonous function of κ, varying as ∝1/k1.11 at a fixed value of Γ, and is found to be independent of Γ at a fixed value of κ. It is observed that for the flow values with MCL&amp;gt;1.5, the shock waves do not travel in the upstream direction but instead form a stationary arc like structure around the obstacle. For the fluid flows with 1≲MCL≲2.6, secondary bow shocks are seen to emerge behind the stationary obstacle which travel in the downstream direction, and the phase velocity of these secondary bow shocks is found to be equal to that of the primary bow shocks.

Passive magnetic shielding in MRI-Linac systems

Passive magnetic shielding refers to the use of ferromagnetic materials to redirect magnetic field lines away from vulnerable regions. An application of particular interest to the medical physics community is shielding in MRI systems, especially integrated MRI-linear accelerator (MRI-Linac) systems. In these systems, the goal is not only to minimize the magnetic field in some volume, but also to minimize the impact of the shield on the magnetic fields within the imaging volume of the MRI scanner.In this work, finite element modelling was used to assess the shielding of a side coupled 6 MV linac and resultant heterogeneity induced within the 30 cm diameter of spherical volume (DSV) of a novel 1 Tesla split bore MRI magnet. A number of different shield parameters were investigated; distance between shield and magnet, shield shape, shield thickness, shield length, openings in the shield, number of concentric layers, spacing between each layer, and shield material. Both the in-line and perpendicular MRI-Linac configurations were studied.By modifying the shield shape around the linac from the starting design of an open ended cylinder, the shielding effect was boosted by approximately 70% whilst the impact on the magnet was simultaneously reduced by approximately 10%. Openings in the shield for the RF port and beam exit were substantial sources of field leakage; however it was demonstrated that shielding could be added around these openings to compensate for this leakage. Layering multiple concentric shield shells was highly effective in the perpendicular configuration, but less so for the in-line configuration. Cautious use of high permeability materials such as Mu-metal can greatly increase the shielding performance in some scenarios. In the perpendicular configuration, magnetic shielding was more effective and the impact on the magnet lower compared with the in-line configuration.

Classical and geometric morphometric methods reveal differences between specimens of Varroa destructor (Mesostigmata: Varroidae) from seven provinces of Iran

Varroa destructor Anderson & Truman is the most serious pest of honey bee colonies all over the world. Its specimens were assessed by morphometric and geometric morphometric methods using six morphometric traits including body length and width, length and width of the right metapodal shield, length of epigynal and the anal shield for classical morphometrics and six landmarks in ventral surface of mite's body, in seven provinces including Ardabil, Markazi, Qom, Qazvin, Alborz, North Khorasan, and Semnan. Twenty and ten individuals were used for morphometric and geometric morphometric studies, respectively. The ventral surface of each mite slide was prepared and used Digimizer and Tps package software for morphometric and geometric morphometric measurements, respectively. Data were analyzed with Past software. Furthermore, principal component analysis (PCA) was used for both two methods. In addition, Cluster analysis was used to categorize specimens of provinces. The results demonstrated significantly morphometric and geometric morphometric (or shape and size) differences among the specimens of provinces. Qazvin and Ardabil were located in one group with the PCA and Cluster analysis in the classical morphometric method and Alborz mite's dimensions showed a significant difference in morphometric measurements with other provinces. However, in the geometric morphometric method, Ardabil, Markazi, North Khorasan, and Semnan specimens were located in another group. The difference in distribution can be related to geographical factors and methods of measurement.

Elevating the Precision of Plasma Probe Diagnostics by Elimination of Bare Probe Protective Shields’ Influence

Probe diagnostics of the low pressure inductive xenon plasma were conducted using classic cylindrical Langmuir probes with conventional protection of their circuits against radio frequency interferences by bare metal shields. The dimensions of their probetips were determined in the special experiment that provided negligible local plasma distortions. Accurate probe measurements were used to determine the spatial plasma parameter distributions in a gas discharge unit of an ion thruster model which helped to develop its ion-extracting grate. The subsequent analysis of probe measurements showed that in these experiments, the plasma electron energy distribution function (EEDF) was quite noticeably deviated from the Maxwell function depending on the main probe shield length that varied from maximum to zero. Use of an additional probe in the special position where its shield was rather long with zero shield length of the main probe showed that the additional shield lowered all plasma parameters. Comparison of both probes’ data identified the principled relationship between measurement errors and EEDF distortions caused by bare probe shield and this dependence was used to correct the initial probe measurements. Therefore plasma probe diagnostics became more precise due to the lowered influence of the bare probe protective shields. Its physical analysis based on previous authors’ works showed that this effect was caused by a shortcircuited double-probe phenomenon in the bare metal shields.

Propagation of monochromatic light in a hot and dense medium

Photons, as quanta of electromagnetic fields, determine the electromagnetic properties of an extremely hot and dense medium. Considering the properties of the photons in the interacting medium of charged particles, we explicitly calculate the electromagnetic properties such as the electric permittivity, magnetic permeability, refractive index and the propagation speed of electromagnetic signals in an extremely hot and dense background. Photons acquire a dynamically generated mass in such a medium. The screening mass of the photon, the Debye shielding length and the plasma frequency are calculated as functions of the statistical parameters of the medium. We study the properties of the propagating particles in astrophysical systems of distinct statistical conditions. The modifications in the properties of the medium lead to the equation of state of the system. We mainly calculate all these parameters for extremely high temperatures of the early universe.

Reproductive features of the deep water hermit crab Sympagurus dimorphus (Anomura: Parapaguridae) inhabiting pseudoshells in the SW Atlantic Ocean

ABSTRACTWe herein provide information on reproductive aspects (the gonopore morphology of both sexes, the size of embryonic eggs and the fecundity) of the hermit crab Sympagurus dimorphus from deep waters of Argentina. Sampling was performed in different oceanographic and fishery campaigns between 2007 and 2010, at 38°01′–39°03′S, 55°–56°05′W, 85–150 m depth, in the SW Atlantic Ocean. Mean shield length (SL) of females was 9.41 ± 1.68 mm (range: 6.6–10.5 mm). Female gonopores measured 0.74 ± 0.10 mm (range: 0.45–0.90 mm), were oval in shape, and were more rounded and larger than male gonopores (0.51 ± 0.007, range: 0.4–0.63 mm). The egg volume for each of the three stages of embryonic development was 0.94 ± 0.20 mm3 for stage I, 1.14 ± 0.31 mm3 for stage II, and 2.07 ± 0.41 mm3 for stage III. Egg volume doubled from the initial to the final stage of the embryonic development. The fecundity (number of eggs) varied from 831 (6.62 mm SL) to 2246 (10 mm SL) for females carrying eggs in stages I+II, and between 158 (158 mm SL) and 1279 (9.4 mm SL) in stage III. The reproductive characteristics of the observed profile are intimately related to S. dimorphus use of a pseudoshell resource and a deep water habitat.