Shield Region Research Articles

Construction of global phase diagrams for binary mixtures with equal and unequal size of molecules by using the modified van der Waals model

The global phase diagram or master diagram is constructed for binary mixtures consist of the equal and unequal size of molecules by using the modified van der Waals model. The Griffiths shield region is also presented on the master diagram. The influence of various size differences ratio of molecules on the master diagram is investigated and discussed. It is observed that the GPD are symmetrical around ζ=0 for the equal-size of molecules and the deterioration in the symmetric behavior of GPD increases as differences of size of molecules increase. From the master diagram, all possible main types of phase behavior for every given interaction energy parameters and various size differences ratio of molecules can be seen directly without long and difficult calculations.

Long-term influence of early human occupations on current forests of the Guiana Shield.

To decipher the long-term influences of pre-Columbian land occupations on contemporary forest structure, diversity, and functioning in Amazonia, most of the previous research focused on the alluvial plains of the major rivers of the Amazon basin. Terra firme, that is, nonflooded forests, particularly from the Guiana Shield, are yet to be explored. In this study, we aim to give new insights into the subtle traces of pre-Columbian influences on present-day forests given the archaeological context of terra firme forests of the Guiana Shield. Following archaeological prospects on 13 sites in French Guiana, we carried out forest inventories inside and outside archaeological sites and assessed the potential pre-Columbian use of the sampled tree species using an original ethnobotanical database of the Guiana Shield region. Aboveground biomass (320 and 380 T/ha, respectively), basal area (25-30 and 30-35m2 /ha, respectively), and tree density (550 and 700 stem/ha, respectively) were all significantly lower on anthropized plots (As) than on nonanthropized plots (NAs). Ancient human presence shaped the species composition of the sampled forests with Arecaceae, Burseraceae, and Lauraceae significantly more frequent in As and Annonaceae and Lecythidaceae more frequent in NAs. Although alpha diversity was not different between As and NAs, the presence of pre-Columbian sites enhances significantly the forest beta diversity at the landscape level. Finally, trees with edible fruits are positively associated with pre-Columbian sites, whereas trees used for construction or for their bark are negatively associated with pre-Columbian sites. Half a millennium after their abandonment, former occupied places from the inner Guiana Shield still bear noticeable differences with nonanthropized places. Considering the lack of data concerning archaeology of terra firme Amazonian forests, our results suggest that pre-Columbian influences on the structure (lower current biomass), diversity (higher beta diversity), and composition (linked to the past human tree uses) of current Amazonian forests might be more important than previously thought.

Design Optimization of 1.2kV 4H-SiC Trench MOSFET

In a trench MOSFET structure, p+ trench bottom implant (also called p+ shielding region) is commonly used to protect the gate oxide from high electric field stress, however, if the design and fabrication process are not optimized properly, the p+ shielding region together with n-drift and the p-base region will form a parasitic JFET which severely degrades the on-state performance of the device. This paper presents this parasitic JFET effect with experimental results and the optimization work that has been done to eliminate the parasitic JFET.

1.2 kV SiC Trench-Gate MOSFETs with Dual Shielding Regions

This paper presents a study of the 1.2kV UMOSFETs with dual shielding regions. Numerical simulations demonstrate the importance of including dual shielding regions to achieve low specific on-resistance and high breakdown voltage. The optimized structure has a low specific on-resistance (Ron,sp) of 2.19 mΩ-cm2, high breakdown voltage of 1470 V, low specific reverse transfer capacitance (Cgd,sp) of 17 pF/cm2 and excellent high-frequency figure-of-merit (HF-FOM) of 37 fs.

Three additional new genera of acidocerine water scavenger beetles from the Guiana and Brazilian Shield regions of South America (Coleoptera, Hydrophilidae, Acidocerinae).

Recent study of the water scavenger beetle subfamily Acidocerinae in the Neotropical region has uncovered numerous undescribed species that are not able to be placed in existing genera. Here, we describe three new genera to accommodate 17 of these new species from South America: Aulonocharesgen. nov. for Aulonochareslingulatussp. nov. (French Guiana, Suriname), Aulonocharesnovoairensissp. nov. (Brazil), and Aulonocharestubulussp. nov. (Brazil, Guyana, Suriname, Venezuela); Ephydrolithusgen. nov. for Ephydrolithushamadaesp. nov. (Brazil), Ephydrolithusminorsp. nov. (Brazil), Ephydrolithusogmossp. nov. (Brazil), Ephydrolithusspiculatussp. nov. (Brazil), and Ephydrolithustelisp. nov. (Brazil); and Primocerusgen. nov. for Primoceruscuspidissp. nov. (Venezuela), Primocerusgigassp. nov. (Venezuela), Primocerusneutrumsp. nov. (Guyana, Suriname, Venezuela), Primocerusocellatussp. nov. (Venezuela), Primoceruspetilussp. nov. (Brazil), Primoceruspijiguaensesp. nov. (Venezuela), Primocerusmaipuresp. nov. (Venezuela), Primocerussemipubescenssp. nov. (Guyana), and Primocerusstriatolatussp. nov. (Suriname). The genus Ephydrolithusgen. nov. is currently known to be restricted to seepages in the mountainous regions of the Brazilian Shield. Aulonocharesgen. nov. and Primocerusgen. nov. are both currently only known from the Guiana Shield, though widespread in that region where they are associated with streams and seeps. We present differential diagnoses, maps, habitat details, and illustrations of all new genera and species here described.

An Optimized p<sup>+ </sup>Shielding 4H-SiC Trench Gate MOSFETs Structure with Floating Regions

In this paper, an optimized p+ shielding 4H-SiC trench-gate metal-oxide-semiconductor field effect transistors (UMOSFETs) structure with floating regions is proposed. The p+ shielding region is moved down to gain a low device on-resistance and the floating regions are designed to improve the breakdown voltage in the proposed structure. Specific on-resistances of the proposed 4H-SiC UMOSFETs is 2.62 mΩ.cm2 at VGS=18 V and VDS=10 V, compared with 4.77 mΩ.cm2 for the conventional p+ shielding UMOSFETs structure with same breakdown voltage. The on-resistance and figure of merit (FOM = VBR2/Ron) improve by 45.1% and 94.2%, respectively.

A novel 4H-SiC trench MOSFET with double shielding structures and ultralow gate-drain charge

A new ultralow gate–drain charge (QGD) 4H-SiC trench MOSFET is presented and its mechanism is investigated by simulation. The novel MOSFET features double shielding structures (DS-MOS): one is the grounded split gate (SG), the other is the P+ shielding region (PSR). Both the SG and the PSR reduce the coupling effect between the gate and the drain, and transform the most part of the gate–drain capacitance (CGD) into the gate–source capacitance (CGS) and drain–source capacitance (CDS) in series. Thus the CGD is reduced and the proposed DS-MOS obtains ultralow QGD. Compared with the double-trench MOSFET (DT-MOS) and the conventional trench MOSFET (CT-MOS), the proposed DS-MOS decreases the QGD by 85% and 81%, respectively. Moreover, the figure of merit (FOM), defined as the product of specific on-resistance (Ron, sp) and QGD (Ron, spQGD), is reduced by 84% and 81%, respectively.

Ball pen probe in strongly magnetised RF plasmas

A study of ball pen probes (BPPs) in a rf strongly magnetised plasma is reported for the first time. These probes have been successfully used in fusion plasmas, with magnetic fields up to 2.5 T, to measure the plasma potential. In this paper experimental results of various ball pen designs (2 and 4 mm diameter with flat and conical collectors) are presented up to 0.5 T in a low pressure capacitively coupled rf plasma. A theory of the BPP is developed, showing that the increase of the collector potential and plateau region, with collector retraction, requires the electron current to decrease faster than the ion current. Experimentally, it is found that to develop effective electron screening the electron Larmor radius should be smaller than the tunnel internal diameter. Smaller tunnels improve screening due to the tunnel entrance wall sheaths. Inside the tunnel a plateau region forms at 81 mT reducing to a broad peak at higher field strengths. Ion shielding and surface losses (for small tunnel diameters) reduce the collector peak width and maximum potential with increasing magnetic field. Conical collectors were found to increase the length of the plateau region and broaden the peak. Particle in cell simulations were in good agreement with the experimental results. The electron shielding and plateau regions were reproduced but not the broad peak at higher field strengths. Good agreement between both 2 mm BPPs and an emissive probe was found only at 81 mT to within 3 V or 1.3 electron temperatures (Te). For all BPPs at higher field strengths (≥ 250 mT) the maximum collector potential underestimated the emissive probe by more than 2.7 Te (7 V). At these field strengths all BPPs agree with each other to within 1.5 Te (4.1 V). Possible reasons for these disagreements are discussed.

On a link of rare earth-rare metal and gold-ore mineralizationwith fault-block tectonics of the Ukrainian shield. 2

In the second article of the cycle «On a link of rare earth-rare metal and gold-ore mineralization with fault-block tectonics of the Ukrainian shield» [Nechaev et al., 2018] the internal structure, kinematics, age and metallogeny of the faults of the Gaivoron-Zavaliev section of the Pobuzhie mining region (PMR) of the Ukrainian shield (USh) have been considered. It is shown that the Gaivoron zone of faults with a width of up to 10 km consists of five shear zones of the latitudinal stretch, which make up the boundary between the Bug and Ros in megablocks of the USh. The kinematic shear zones are laid out as left shifts in the field of stresses σ 1 45°, σ 3 315°, σ 2 ∟ (West-Ingulets stage). The youngest stage of their activization is the Subbotsk-Moshorin (σ 1 312°, σ 3 42°, σ 2 ∟ — right shift). The actual Gaivoron shear zone is characterized by widespread lamprophyres with rare earth mineralization of La, Ce, Y, as well as increased content of Ti, Mn, Ba, Cr. Within the Khaschevat shear zone the Solomievsk deposit of aqueous phosphates with yttrium composition of ores and an iron-manganese deposit with a priority triad of Y, Yb, Ge, as well as Au are known among tectonites. The granitoids of the Ustye-Stavsk shear zone are characterized by an abnormally high monazite content. For the first time the internal structure and kinematics of the Zavaliev fault zone, the width of which is at least 4 km, is studied in detail. It is shown that it consists of two shear zones — the latitudinal actually Zavaliev and northeastern Peschanaya-Zhakchik. Both shear zones are observed in the Zavaliev graphite pit. The yformed, as the Gaivoron zone of faults, at the West-Ingulets stage, and the last phase of activіzation took place in the Subbotsk-Moshorin stage. The opinion that the Zavaliev structure is not a synclinal fold, as was supposed to be, but an intrafault lens of hydrothermalites-metasomatites. These include graphite-biotite gneisses and shales, ore and ore-free quartzites, calciphyres and skarnoids. In addition to the world’s reserves of graphite, elevated concentrations of gold, silver, platinum, and iridium are widely represented in the zone of faults (in zones of silicification and sulfidization of graphite-biotite gneisses).

A Revision of Cuphea section Amazoniana s. s. (Lythraceae)

Abstract—Cuphea section Amazoniana, one of 13 sections in Cuphea, comprises 20 species, mostly narrow endemics in Colombia, Ecuador, and the Guiana Shield region of Venezuela, Guyana, French Guiana, and Brazil. The species inhabit river margins, tepuis, scrubland, savanna, and low montane forests in tropical to cold temperate climates. They are subshrubs defined by the common presence of a strigose indumentum of bifid (malpighiaceous) trichomes; small elliptic to narrowly lanceolate or linear coriaceous leaves; and tubular flowers to 9 mm long with 11 deeply inserted stamens included in the floral tube. In morphology, they are similar to or partially overlap species currently classified in Cuphea sections Trispermum and Heteranthus. The revision provides a new key, comparative morphological descriptions, first descriptions and illustrations of pollen and seed morphology, and distribution maps. Cuphea saxatilis S. A. Graham, sp. nov. from Colombia and Cuphea trisperma S. A. Graham, sp. nov. from Venezuela are newly described. Cuphea killipii Lourteig is placed in synonomy of C. philombria Lourteig. Presence or absence of a floral spur, position and shape of a nectary-like floral organ, the “disc”, and presence of two major pollen types suggest the section is not monophyletic, but consists of a minimum of two phylogenetic lineages, one in the Guiana Shield region in Venezuela and eastward, the other in low montane forests and on outliers of the Guiana Shield in Colombia and northern Ecuador. Fossilized Cuphea pollen grains resembling two types of pollen known in sect. Amazoniana, establish the presence of the genus in the Mio-Pliocene to Holocene of northern South America in areas occupied today by members of the section.

An Improved 4H-SiC Trench MOS Barrier Schottky Diode With Lower On-Resistance

An improved 4H-SiC trench MOS barrier Schottky (TMBS) structure that can significantly reduce the specific on-resistance ( $R_{on,sp}$ ) is proposed in this paper. Compared with the conventional TMBS structure, an N-type region is added around the P+ shielding region and along the trench sidewall in the proposed structure, and the doping concentration is higher than that of the drift region. The JFET resistance, and spread resistance can both be reduced significantly during the forward bias to produce a much lower $R_{on,sp}$ , which have been verified through the numeric simulations and modeling analysis. The critical parameters (N-type region width and its doping concentration) of the proposed structure are mainly optimized by the ATLAS simulation tool. As a result, the breakdown voltage and leakage current of the improved structure remain basically unchanged compared with the conventional TMBS. However, the $R_{on,sp}$ and FoM ( BV 2/ $R_{on,sp}$ ) can be effectively improved by 41.9% and 70.9%, respectively.

ЗАКОНОМІРНОСТІ ЗВ'ЯЗКІВ МІЖ ПОТУЖНОСТЯМИ І ПОШИРЕНОСТЯМИ ТЕРИГЕННИХ ВІДКЛАДІВ НА ПРИКЛАДІ ОСАДОВОГО ЧОХЛА ПІВНОЧІ УКРАЇНСЬКОГО ЩИТА

This article focuses on identifying patterns typical for formations of sediment stratum that covers crystalline foundation in the north of Ukrainian shield, and on their basisfinding new methods that could be used during regional research, and also while exploring and prospecting sediment minerals fields. In particular, there are researches of statistical relations between average thickness and spreading of terrigenous sediments using the example of two territories situated on Novograd block of Volyn mega block and Fastiv block of Rosynsk-Tikytsk mega block. For this purpose, method of double correlation analysis was used. It was found out that there are various correlation connections between these indexes for the whole stratum, Quaternary and Neogene deposits. Part of them has strong and very strong relative connections. The following pattern was identified: in relatively well sorted or not sorted sediments correlational connection between thickness and spreading is always stronger than in all the sediments together in the case when they form the bigger part of sediment stratum volume or the volume of its researched part. Thus, one of the main factors that influence the correlational connections between thickness and spreading of all the sediment stratum or its part is their sorted or unsorted state. The information about existence of strong correlation connections between thickness and spreading of sediments of all the sediment stratum or its part can makegeological or sedimentological maps more substantial if they reflect spreading of these sediments. In this case according to the region of spreading of a sediment one can make at least qualitative evaluation of its average thickness, and thus its volume on the territory that is shown on the map. The identified pattern can be used while calculating projected resources of some minerals in some fields, zones, areas of their spreading. First of all, it concerns minerals that form separate horizons. They are secondary kaolin, expanded and bentonite clay, brown coal etc. With the help of this pattern one can calculate mineragenic potential in separate topographical sheets, administrative and geomorphological areas etc. The research of correlation connections between sediment thickness and spreading on the other mega blocks of Ukrainian shield and other regions may be perspective.

40Ar/39Ar Geochronology of the Malyy (Little) Murun Massif, Aldan Shield of the Siberian Craton: A Simple Story for an Intricate Igneous Complex

The Malyy (Little) Murun massif of the Aldan Shield of the Siberian Craton has long been a kind of Siberian Mecca for geologists. It has attracted thousands of geologists, prospectors, and mineral collectors despite its remote location. It is famous for a dozen new and rare minerals, including the gemstones charoite and dianite (the latter is the market name for strontian potassicrichrerite), as well as for a range of uncommon alkaline igneous rocks. Despite this, the age of the Malyy Murun igneous complex and associated metasomatic and hydrothermal mineral associations has remained poorly constrained until now. In this paper, we provide extensive 40Ar/39Ar geochronological data to reveal its age and temporal history. It appears that, although unique in terms of rocks and constituent minerals, the Malyy Murun is just one of multiple alkaline massifs and lavas emplaced in the Early Cretaceous (~137–128 Ma) within a framework of the extensional setting of the Aldan Shield and nearby Transbaikalian region. The extension took place 40–60 million years after the supposed closure of the Mongolia–Okhotsk Ocean and orogenic peak in the Early–Middle Jurassic.

Conductive Layer Modeling by Improved Second-Order Artificial Material Single-Layer Method

An improved second-order artificial material single-layer (AMSL) method is proposed to predict the electromagnetic field in the presence of conductive thin layers by the finite-element method (FEM). The AMSL method is based on the replacement of the material physical constants of a conductive shield region with those of an artificial material. The new AMSL physical constants are analytically extracted by equating the equivalent transmission line equations governing the field propagation inside the shield with the FEM solution. This new formulation of the method is a significant improvement of the original AMSL as it is much more robust and accurate for near field solutions, and, above all, it is much more easily implementable in commercial software tools.

A new species of Vanilla (Orchidaceae) from the North West Amazon in Colombia

A distinctive species, Vanilla denshikoira, is described from the North West Amazon, in Colombia, within the Guiana Shield region. The species has morphological features similar to those of species in the Vanilla planifolia group. It is an important addition to the vanilla crop wild relatives, bringing the total number of species in the V. planifolia group to 21. Vanilla denshikoira is a narrow endemic, known from only a single locality, and highly vulnerable to anthropological disturbance. Under IUCN criteria it is categorized CR. The species has potential value as a non-timber forest product. We recommend a conservation program that includes support for circa situm actions implemented by the local communities.

Effect of P+ shielding region on single event burnout of 4H[sbnd]SiC trench gate MOSFET

In this work, numerical simulation methods have been applied to a 4HSiC trench-gate MOSFET structure to investigate its susceptibility to single event burnout. With SILVACO ATLAS, the high-k shielded trench-gate MOSFET and high-k trench-gate MOSFET are investigated to prove that P+ shielding region under the trench bottom could provide a leaking path of hole current and improve the device's tolerance to single-event burnout. The simulation results show that the using of P+ shielding region makes the burnout threshold voltage change from 360 V in high-k trench-gate MOSFET to 470 V in high-k shielded trench-gate MOSFET, about 30.6% improvement in the performance of SEB.

The effects of the pressure outlet's position on the diffusion and pollution of dust in tunnel using a shield tunneling machine

In order to gain a more in-depth knowledge of a shield machine's dust-suppression ventilation system, this paper uses the shield region on the south side of the No. 8 Subway from Jiaodong International Airport, Qingdao, China, as a case study, and conducts field measurements and numerical simulations for examining dust concentration distributions in a tunnel when the ventilation system is not in operation (i.e., under single-pressure conditions) and when the air pressure cylinder is in operation (specifically, the distance between the pressure outlet-2 and the cutter, denoted as Lp, was set at different values within a range of 30∼75 m). The results reveal that under single-pressure conditions, dust was diffused throughout the entire tunnel and caused serious pollution. After the ventilation system was opened: when Lp < 50 m, the use of a ventilation system could not control the diffusion of dust effectively, and its dust-suppression performance was enhanced with the increase of Lp; when 50 m ≤ Lp ≤ 55 m, its dust suppression performance was relatively optimal, but some dust still spread to the operating region; when Lp > 70 m, a low-velocity airflow belt was formed in the operating range of 25∼30 m, i.e., the ventilation requirements could not be satisfied; and when 60 m ≤ Lp ≤ 70 m, both the ventilation and optimal dust suppression performance could be achieved simultaneously.

Palladium Acetate Revisited: Unusual Ring-Current Effects, One-Electron Reduction, and Metal-Metal Bonding.

Palladium(II) acetate (1) and two new complexes of the ligand α,α,α',α'-tetramethyl-1,3-benzenedipropionate (esp2-), C s-Pd3(esp)3 ( Cs-2) and C3 h-Pd3(esp)3 ( C3 h-2), are studied in the solid state and in solution. Variable-temperature NMR and DFT studies of C s-2 reveal an unusual shielding region above the Pd atoms. The compounds show a surprising quasi-reversible reduction between -880 and -1200 mV versus Fc/Fc+, and the Pd3(esp)3 complexes may be cleanly reduced electrochemically. EPR spectra of reduced samples show pseudo-axial signals with 105Pd hyperfine coupling, consistent with unprecedented, isostructural Pd35+ species with a valence-trapped PdII-PdII-PdI electronic structure.

Structural Elucidation of Peanut, Sunflower and Gingelly Oils by Using FTIR and 1H NMR Spectroscopy

Aims: The present study focused on FTIR and 1H-NMR spectroscopic methods to assign structural connectivity and purity of the oils. Methods: Non-destructive Fourier Transform Infrared (FTIR) and 1H nuclear magnetic resonance (1H-NMR) spectroscopy techniques are used to assign the structural confirmation of the triacylglyceride (TAG) functional component in three different oils namely Sunflower, Peanut, and Gingelly oils respectively. Results: FTIR spectrum shows a very high intense band at 1744 cm-1 associated with the existence of the ester carbonyl functional group (O-C=O) and very weak shoulder peak of cis double-bond (C=C) stretching was noticed at ∼1655 cm-1. In 1H-NMR spectrum shows well resolved chemical shift values in the range 5.3-0.8 ppm corresponding to characteristic group in aliphatic region. Conclusion: Each distinct peak was determined based on chemical shift as well as splitting pattern values. For olefin signal as triplet, tertiary methine protons as singlet, well separated oxymethylene seen as triplet at ~4.2 ppm owing to presence of high electronegative oxygen atom connected to methylene chain gives more deshielding effect. As for bis-allylic, α-carbonyl methylene, β-carbonyl methylene, allylic, saturated methylene along with terminal methyl proton signals are noticed in the span of 2.3-0.8 ppm. A remarkable feature of the spectra is well resolved chemical shift values is clearly support presence of longer hydrocarbon chains. Absence of multiplet coupling peaks and disappearance of signals in down shield region > 5.4 ppm confirms the absence of trans stereoisomer (E-conformation), aromatic and heterocyclic epoxide compounds.

Malakit: an innovative pilot project to self-diagnose and self-treat malaria among illegal gold miners in the Guiana Shield

BackgroundIllegal gold miners in French Guiana, a French overseas territory (‘département’) located in Amazonia, often carry malaria parasites (up to 46.8%). While the Guiana Shield Region aims at malaria elimination, the high prevalence of Plasmodium in this hard-to-reach population in conjunction with frequent incorrect use of artemisinin-based anti-malarials could favour the emergence of resistant parasites. Due to geographical and regulatory issues in French Guiana, usual malaria control strategies cannot be implemented in this particular context. Therefore, new strategies targeting this specific population in the forest are required.MethodsNumerous discussions among health institutions and scientific partners from French Guiana, Brazil and Suriname have led to an innovative project based on the distribution of kits for self-diagnosis and self-treatment of Plasmodium infections. The kit-distribution will be implemented at “resting sites”, which are areas across the border of French Guiana regularly frequented by gold miners. The main objective is to increase the appropriate use and complete malaria treatment after a positive malaria diagnosis with a rapid test, which will be evaluated with before-and-after cross-sectional studies. Monitoring indicators will be collected from health mediators at the time of kit distribution and during subsequent visits, and from illegal gold miners themselves, through a smartphone application. The project funding is multisource, including Ministries of Health of the three countries, WHO/PAHO, and the European Union.ResultsThis project will start in April 2018 as a 18 month pilot study led by the Clinical Investigation Centre of Cayenne. Results should be available at the end of 2019.DiscussionThis innovative approach may have several limitations which should be taken into account, as potential side effects, kit misuse or resale, declarative main criteria, or no Plasmodium vivax curative treatment. Close monitoring is thus needed.ConclusionsThis project may be the best available solution to a specific and important public health challenge in the Guiana Shield. If the use of self-diagnosis and self-treatment approach is effective, this strategy could be sustained by health institutions in the region.