Small Shield Research Articles

STRUCTURAL AND DIELECTRIC EVOLUTION OF COBALT FERRITE NANOPARTICLES FOR MICROWAVE APPLICATIONS

In this paper, coprecipitation method was used in the synthesis of cobalt ferrite nano particles, while investigations were carried out to determine the effect of sintering temperature on the structural and dielectric properties of the prepared samples. The structural/morphological and dielectric properties of the products were determined by X-raydiffraction (XRD), transmission electron microscopy (TEM), and open ended coaxial probe (OECP). Results from analysis confirms that heat treatment influences the magnitude of dielectric constant and the structural evolution of the samples. TEM mages reveal that the samples surfaces exhibit well-defined crystalline nanoparticles of spherical shapes with small agglomeration at higher sintering temperature while the sizes of the particles increases with annealing temperature due to grain boundary growth. The magnitude of dielectric constant was influenced by interfacial polarization as well as iron hopping of Fe2+ to Fe3+ and Co2+ to Co3+ at B-sites. Sintering temperature also influenced the dielectric characteristics, and this is confirmed from the dielectric measurements at room temperature. Based on the result obtained for dielectric constant, these samples are suitable for small microwave shielding.

Geological Characterization of the Ina Shield Volcano Summit Pit Crater on the Moon: Evidence for Extrusion of Waning‐Stage Lava Lake Magmatic Foams and Anomalously Young Crater Retention Ages

AbstractIna, a distinctive ~2 × 3 km D‐shaped depression, is composed of unusual bulbous‐shaped mounds surrounded by optically immature hummocky/blocky floor units. The crisp appearance, optical immaturity, and low number of superposed impact craters combine to strongly suggest a geologically recent formation for Ina, but the specific formation mechanism remains controversial. We reconfirm that Ina is a summit pit crater/vent on a small shield volcano ~3.5 billion years old. Following detailed characterization, we interpret the range of Ina characteristics to be consistent with a two‐component model of origin during the waning stages of summit pit eruption activities. The Ina pit crater floor is interpreted to be dominated by the products of late‐stage, low‐rise rate magmatic dike emplacement. Magma in the dike underwent significant shallow degassing and vesicle formation, followed by continued degassing below the solidified and highly microvesicular and macrovesicular lava lake crust, resulting in cracking of the crust and extrusion of gas‐rich magmatic foams onto the lava lake crust to form the mounds. These unique substrate characteristics (highly porous aerogel‐like foam mounds and floor terrains with large vesicles and void space) exert important effects on subsequent impact crater characteristics and populations, influencing (1) optical maturation processes, (2) regolith development, and (3) landscape evolution by modifying the nature and evolution of superposed impact craters and thus producing anomalously young crater retention ages. Accounting for these effects results in a shift of crater size‐frequency distribution model ages from <100 million years to ~3.5 billion years, contemporaneous with the underlying ancient shield volcano.

The effect of railway platforms and platform canopies on sound propagation

The effect of railway platforms on sound propagation has thus far not been investigated in detail. Due to the vicinity to the track, the platform’s large reflecting horizontal surface, and the often present canopy it is unclear whether standard noise propagation prediction methods can be applied without modifications. Here, the acoustic effect of low railway platforms was investigated using measurements directly at the platform as well as in the distance in order to derive suitable models for the 2.5D boundary element method (BEM) as well as for standardized prediction methods. For the BEM using a source at the center of the track at the height of the platform edge was found to be an optimal solution. Different standard platform variations were investigated. The results show a relatively small, low lying, and localized shielding effect of the platform of up to 3 dB that further diminishes with increasing platform width. In comparison, a low noise barrier at the same position yields up to 4 dB and the effect is less localized. Although a canopy may lead to a better protection of elevated positions, the presence of such a structure also leads to a further decrease of the platform shielding in lower positions. Absorption on the lower side of the canopy can reduce this undesirable effect, however, only when large portions of the canopy are covered with absorbing material. Using the BE calculations and the measurements, two standardized calculation schemes, i.e. the Austrian ONR 305011 and the noise assessment methods defined in the European Directive 2015/996 (EU) were investigated. Both methods overestimate the platform effect. Similar to the BEM, a better agreement is reached when the source position is adjusted to the platform height. Floating elements such as a canopy are not defined in any of these standards, however, non-standard calculations of such objects as already implemented in certain noise mapping software could be used to take into account the attenuation effect for certain receiver positions.

Alkali-Metal-Intercalated Percolation Network Regulates Self-Assembled Electronic Aromatic Molecules.

In the continuously growing field of correlated electronic molecular crystals, there is significant interest in addressing alkali-metal-intercalated aromatic hydrocarbons, in which the possibility of high-temperature superconductivity emerges. However, searching for superconducting aromatic molecular crystals remains elusive due to their small shielding fraction volume. To exploit this potential, a design principle for percolation networks of technologically important film geometry is indispensable. Here the effect of potassium-intercalation is shown on the percolation network in self-assembled aromatic molecular crystals. It is demonstrated that one-dimensional (1D) dipole pairs, induced by dipole interaction, regulate the conductivity, as well as the electronic and optical transitions, in alkali-metal-intercalated molecular electronic crystals. A solid-solution growth methodology of aromatic molecular films with a broad range of stability is developed to uncover electronic and optical transitions of technological importance. The light-induced electron interactions enhance the charge-carrier itinerancy, leading to a switchable metal-to-insulator transition. This discovery opens a route for the development of aromatic molecular electronic solids and long-term modulation of electronic efficacy in nanotechnologically important thin films.

The volcanic association of Las Lomadas area, Corona Chico Volcanites. Somún Curá Magmatism. Río Negro province, Argentina

This contribution deals with the Corona Chico Vulcanites, within the Somun Cura Magmatic Province, northern Extra-Andean Patagonia. The studied area is located to the north of the Alta Sierra de Somun Cura Volcanic Complex and is made of several basaltic volcanic buildings of varied morphologies: spatter cones, tuff ring and long lava flows related to small shield volcanoes (of scutulum type). Petrographic characteristics as well as whole rock chemical composition suggest a time progressive increase in alkalis content and a shift from early transitional terms to basanitic rocks in the latest stages. A simulation of the source yielded for Las Lomadas rocks an astenospheric source in the garnet-spinel facies, with associated low partial melting percentages (< 7-8%). Within the studied rock set, the spatter cones sequence displays geochemical affinities with the basaltic component of Alta Sierra de Somun Cura Volcanic Complex.

A neutron beam monitor based on silicon carbide semiconductor coated with 6LiF converter

A neutron beam monitor was developed for the time-of-flight neutron reflectometer (NR) instrument at the China Mianyang Research Reactor (CMRR). The SiC neutron monitor employs a wide-bandgap silicon carbide (SiC) semiconductor detector coated with a 6LiF neutron converter film evaporated on a thin ceramic sheet. Given the relatively large active area [(10 × 10) mm2] and sufficiently thick epitaxial layer (30μm), the monitor can discriminate the gamma background from the signals. Prior to assembling the monitor, the I–V characteristics and alpha responses of the SiC detector were measured. Next, the SiC detector and 6LiF neutron converter were installed in a small aluminum shielding box, and the neutron and gamma responses were measured with an Am–Li neutron source and a 137Cs plus 60Co gamma source, respectively. The fabricated SiC neutron monitor was mounted inside the slit of the NR instrument (after the focusing neutron guide), and the intensity of the transmitted neutron beam was measured. To measure the incident neutron flux, the distinct triton peaks from the 6Li (n, α) T reaction were counted as normalized data for the NR instrument. This paper describes the fabrication details of the SiC neutron monitor, and discusses the preliminary measurements.

A wideband circularly polarized cross‐shaped linearly tapered slot antenna

AbstractA new method to realize wideband circular polarization base on cross‐shaped TSA (tapered slot antenna) is proposed. The proposed antenna is obtained by integrating a wideband feed network and two cross placed loaded linearly TSAs (LLTSAs) together. Taking low‐cost, compact structure, and small shielding effect into consideration, a traditional planar feed network is divided into two parts and designed in cross‐shaped form. Loading structures are applied to suppress back radiation of the antenna. The antenna is simulated and tested. The results indicate that a − 10 dB reflection coefficient bandwidth of 109% (3.5‐11.9 GHz) and an axial ratio (AR) bandwidth of 92.5% (3.6‐9.8 GHz) for AR ≤ 3 dB are obtained. The simulated results exhibit that higher Front‐to‐Back Ratio (FBR) across the whole 3‐dB AR bandwidth can be obtained by loading. Moreover, a stable gain of 5.5 ± 0.1 dB is achieved from 7.5 GHz to 9.8 GHz.

Controls on Lunar Basaltic Volcanic Eruption Structure and Morphology: Gas Release Patterns in Sequential Eruption Phases

AbstractAssessment of mare basalt gas release patterns during individual eruptions provides the basis for predicting the effect of vesiculation processes on the structure and morphology of associated features. We subdivide typical lunar eruptions into four phases: Phase 1, dike penetrates to the surface, transient gas release phase; Phase 2, dike base still rising, high‐flux hawaiian eruptive phase; Phase 3, dike equilibration, lower flux hawaiian to strombolian transition phase; and Phase 4, dike closing, strombolian vesicular flow phase. We show how these four phases of mare basalt volatile release, together with total dike volumes, initial magma volatile content, vent configuration, and magma discharge rate, can help relate the wide range of apparently disparate lunar volcanic features (pyroclastic mantles, small shield volcanoes, compound flow fields, sinuous rilles, long lava flows, pyroclastic cones, summit pit craters, irregular mare patches, and ring moat dome structures) to a common set of eruption processes.

Radiation characterisation and dosimetric measurements of a femtosecond pulsed laser ablation system

This work describes the radiation characterisation and dosimetric measurements performed on the low-energy micromachining station of the femtosecond STELA (Santiago TErawatt LAser) at the University of Santiago de Compostela (Spain). For this aim, ionisation chambers, solid state detectors, and radiochromic films were used. The results show the emission of pulsed x-ray produced by laser-accelerated electrons from the ablated material exhibiting both bremsstrahlung and characteristic radiation. Although this radiation was produced unintentionally, a high superficial dose rate can be achieved. This radiation can be successfully stopped using small shielding to protect personnel from its effects. Based on the results of this work, the yearly dose equivalent after installing the shielding was negligible.

Small molecules shield mice against hearing loss

Small molecules shield mice against hearing loss

监控系统在油气管道小断面盾构工程中的应用

监控系统在油气管道小断面盾构工程中的应用

小断面盾构施工项目签证索赔管理探究

小断面盾构施工项目签证索赔管理探究

小型盾构始发场地的规划建设

小型盾构始发场地的规划建设

Climate change alters the quantity and phenology of habitat for lake trout (Salvelinus namaycush) in small Boreal Shield lakes

We analyzed monitoring data (1970–2013) from small Boreal Shield lakes to understand how variations in air temperature and precipitation affect the phenology and amount of habitat for lake trout (Salvelinus namaycush). Annual air temperatures increased by ∼2 °C (significant in fall and winter). In response, ice cover was reduced by ∼19 days. Despite earlier ice-offs, springs became longer, allowing lake trout longer access to littoral regions when water temperatures were cool. Although summer surface water temperatures increased, the summer did not lengthen. Instead, later spring-warming and fall-cooling of lakes caused summer to shift later in the year, potentially delaying fall spawning. Complete loss of optimal oxythermal habitat volume occurred in all lakes and became more prevalent over time, more so in the darkest lakes. Although air temperatures did not become more variable, several habitat measures did, including mean summer surface water temperatures, duration of ice cover, timing of ice-off, and minimum volumes of optimal oxythermal habitat. Our results suggest that future warming will impose greater thermal stress on lake trout, but may be tempered by longer springs.

A new species of Rhinophis Hemprich, 1820 (Serpentes: Uropeltidae) from the central hills of Sri Lanka.

A new species of uropeltid snake, Rhinophis roshanpererai sp. nov., is described based on three specimens from Badulla District, Sri Lanka. The new species is distinguished from its congeners by the number of dorsal scale rows and ventral scales, a colour pattern that lacks pale stripes, and by having a very small tail shield with four or three prominent spines. Based on lack of records from similar habitats and elevations elsewhere in Sri Lanka, the new species likely has a very small range in the central highlands. The description of the new species brings the total nominal species of Rhinophis to 20, with four of the 16 Sri Lankan species having been described since 2009.

Plateaus and sinuous ridges as the fingerprints of lava flow inflation in the Eastern Tharsis Plains of Mars

The Tharsis Montes rift aprons are composed of outpourings of lava from chaotic terrains to the northeast and southwest flank of each volcano. Sinuous and branching channel networks that are present on the rift aprons suggest the possibility of fluvial processes in their development, or erosion by rapidly emplaced lavas, but the style of lava flow emplacement throughout rift apron development is not clearly understood. To better characterize the style of lava emplacement and role of fluvial processes in rift apron development, we conducted morphological mapping of the Pavonis Mons southwest rift apron and the eastern Tharsis plains using images from the High Resolution Imaging Science Experiment (HiRISE), Mars Orbiter Camera (MOC), Context Camera (CTX), Thermal Emission Imaging System (THEMIS), and High Resolution Stereo Camera (HRSC) along with the Mars Orbiter Laser Altimeter (MOLA) Precision Experiment Data Records (PEDRs) and gridded data. Our approach was to: (1) search for depositional fans at the slope break between the rift apron and adjacent low slope plains; (2) determine if there is evidence that previously formed deposits might have been buried by plains units; (3) characterize the Tharsis plains morphologies east of Pavonis Mons; and (4) assess their relationship to the rift apron units. We have not identified topographically significant depositional fans, nor did we observe evidence to suggest that plains units have buried older rift apron units. Flow features associated with the rift apron are observed to continue across the slope break onto the plains. In this area, the plains are composed of a variety of small fissures and low shield vents around which broad channel-fed and tube-fed flows have been identified. We also find broad, flat-topped plateaus and sinuous ridges mixed among the channels, tubes and vents. Flat-topped plateaus and sinuous ridges are morphologies that are analogous to those observed on the coastal plain of Hawai‘i, where lava flows have advanced from the volcano's several degree flank onto the nearly zero degree coastal plain. When local volumetric flow rates are low, flow fronts tend to spread laterally and often thicken via endogenous growth, or inflation, of the sheet-like flow units. If flow advance is restricted by existing topography into narrow pathways, inflation can be focused into sinuous, elongate ridges. The presence of plateaus and ridges—emplaced from the rift zones, across the plains to the east of Pavonis Mons—and a lack of fan-like features, or evidence for their burial, are consistent with rift apron lavas crossing a slope break with low local volumetric flow rates that led to inflation of sheet-like and tube-fed lava flows.

Opposing Transcriptional Mechanisms Regulate Toxoplasma Development.

The Toxoplasma biology that underlies human chronic infection is developmental conversion of the acute tachyzoite stage into the latent bradyzoite stage. We investigated the roles of two alkaline-stress-induced ApiAP2 transcription factors, AP2IV-3 and AP2IX-9, in bradyzoite development. These factors were expressed in two overlapping waves during bradyzoite development, with AP2IX-9 increasing expression earlier than AP2IV-3, which peaked as AP2IX-9 expression was declining. Disruption of the AP2IX-9 gene enhanced, while deletion of AP2IV-3 gene decreased, tissue cyst formation, demonstrating that these factors have opposite functions in bradyzoite development. Conversely, conditional overexpression of FKBP-modified AP2IX-9 or AP2IV-3 with the small molecule Shield 1 had a reciprocal effect on tissue cyst formation, confirming the conclusions of the knockout experiments. The AP2IX-9 repressor and AP2IV-3 activator tissue cyst phenotypes were borne out in gene expression studies that determined that many of the same bradyzoite genes were regulated in an opposite manner by these transcription factors. A common gene target was the canonical bradyzoite marker BAG1, and mechanistic experiments determined that, like AP2IX-9, AP2IV-3 regulates a BAG1 promoter-luciferase reporter and specifically binds the BAG1 promoter in parasite chromatin. Altogether, these results suggest that the AP2IX-9 transcriptional repressor and the AP2IV-3 transcriptional activator likely compete to control bradyzoite gene expression, which may permit Toxoplasma to better adapt to different tissue environments and select a suitable host cell for long-term survival of the dormant tissue cyst. IMPORTANCEToxoplasma infections are lifelong because of the development of the bradyzoite tissue cyst, which is effectively invisible to the immune system. Despite the important clinical consequences of this developmental pathway, the molecular basis of the switch mechanisms that control tissue cyst formation is still poorly understood. Significant changes in gene expression are associated with tissue cyst development, and ApiAP2 transcription factors are an important mechanism regulating this developmental transcriptome. However, the molecular composition of these ApiAP2 complexes and the operating principles of ApiAP2 mechanisms are not well defined. Here we establish that competing ApiAP2 transcriptional mechanisms operate to regulate this clinically important developmental pathway.

Eruption of magmatic foams on the Moon: Formation in the waning stages of dike emplacement events as an explanation of “irregular mare patches”

Volcanic eruptions on the Moon take place in conditions of low gravity and negligible atmospheric pressure, very different from those on Earth. These differences lead to characteristic lunar versions of hawaiian and strombolian explosive activity, and to the production of unusual eruption products neither predicted nor observed on Earth in the terminal stages of eruptions. These include the unusual mounds and rough (hummocky, blocky) floors of some small-shield summit pit crater floors, elongate depressions and mare flows (similar to those named “irregular mare patches”, IMPs, by Braden et al., 2014). We examine the ascent and eruption of magma in the waning stages of the eruptive process in small-shield summit pit crater floors and show that many IMP characteristics can be plausibly explained by basaltic magma behavior as the rise rate of the ascending magma slows to zero, volatiles exsolve in the dike and lava lake to form a very vesicular foam, and the dike begins to close. Stresses in the very vesicular and porous lava lake crust produce fractures through which the foam extrudes at a rate determined by its non-Newtonian rheology. Waning-stage extrusion of viscous magmatic foams to the surface produces convex mounds whose physical properties inhibit typical impact crater formation and regolith development, creating an artificially young crater retention age. This mechanism for the production and extrusion of very vesicular magmatic foams is also applicable to waning-stage dike closure associated with pit craters atop dikes, and fissure eruptions in the lunar maria, providing an explanation for many irregular mare patches. This mechanism implies that IMPs and associated mare structures (small shields, pit craters and fissure flows) formed synchronously billions of years ago, in contrast to very young ages (less than ~100millionyears) proposed for IMPs by some workers.

Melting the lithosphere: Metasomes as a source for mantle-derived magmas

Peridotite constitutes most of the Earth's upper mantle, and it is therefore unsurprising that most mantle-derived magmas exhibit evidence of past equilibrium with an olivine-dominated source. Although there is mounting evidence for the role of pyroxenite in magma generation within upwelling mantle plumes, a less documented non-peridotite source of melts are metasomatic veins (metasomes) within the lithospheric mantle. Here we present major and trace element analyses of 66 lavas erupted from a small Miocene shield volcano located within the Ethiopian flood basalt province. Erupted lavas are intercalated with lahars and pyroclastic horizons that are overlain by a later stage of activity manifested in small cinder cones and flows. The lavas form two distinctive petrographic and geochemical groups: (A) an olivine–phyric, low Ti group (1.7–2.7 wt.% TiO2; 4.0–13.6 wt.% MgO), which geochemically resembles most of the basalts in the region. These low Ti lavas are the only geochemical units identified in the later cinder cones and associated lava flows; (B) a clinopyroxene–phyric high Ti group (3.1–6.5 wt.% TiO2; 2.8–9.2 wt.% MgO), which resembles the Oligocene HT-2 flood basalts. This unit is found intercalated with low Ti lavas within the Miocene shield. In comparison to the low Ti group, the high Ti lavas exhibit a profound depletion in Ni, Cr, Al, and Si, and significant enrichment in Ca, Fe, V, and the most incompatible trace elements. A characteristic negative K anomaly in primitive-mantle normalized diagrams, and Na2O>K2O, suggests a source rich in amphibole, devoid of olivine, and perhaps containing some carbonate and magnetite. While melt generation during rift development in Ethiopia is strongly correlated with the thermo-chemical anomalies associated with the African Superplume, thermobaric destabilization and melting of mantle metasomes may also contribute to lithospheric thinning. In regions impacted by mantle plumes, such melts may be critical to weakening of the continental lithosphere and the development of rifts.

Identification of Fungal Species Associated with Branch Dieback of Olive and Resistance of Table Cultivars to Neofusicoccum mediterraneum and Botryosphaeria dothidea.

Over two consecutive seasons, 16 olive orchards with trees exhibiting dieback symptoms on branches were surveyed in southern Spain. The six dominant fungal species recovered were characterized by means of phenotypic observations, DNA analysis (by sequencing of the internal transcribed spacer, β-tubulin, and large subunit nuclear ribosomal DNA regions), and pathogenicity tests. Additionally, three isolates collected from Tunisian olive trees showing similar dieback symptoms, one isolate of Colletotrichum godetiae, and a reference isolates of Neofusicoccum mediterraneum were included. The resistance of the 11 most important table cultivars to N. mediterraneum and Botryosphaeria dothidea, the causal agent of "escudete" (small shield) of fruit, was studied by the inoculation of branches and immature fruit, respectively. The species Cytospora pruinosa, N. mediterraneum, Nothophoma quercina, Comoclathris incompta, and Diaporthe sp. were identified. Only N. mediterraneum and C. incompta were able to induce the typical dieback symptoms and cankers that affected the development of the plants. The species N. mediterraneum was the most virulent among the evaluated species, although differences in virulence among its isolates were observed. The remaining fungal species were weakly pathogenic to nonpathogenic on plants. According to resistance tests, 'Gordal Sevillana' and 'Manzanilla Cacereña' were the most susceptible to branch dieback caused by N. mediterraneum. Furthermore, the fruit of 'Aloreña de Atarfe' and 'Manzanilla de Sevilla' were the most susceptible to B. dothidea. Knowledge of the etiology and cultivar resistance of these diseases will help to establish better control measures.