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Number of results: 7
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Abstract

This paper presents a review of models of the current transport in different kind of heterojunctions (HJs) and their characteristics. In order to effectively deduce the dominant electron transport for the HJs based on ZnO or Zn1−xMgxO layers grown on Si substrate by MBE a comparison is performed – which type of the HJ exhibits better electrical properties. The current–voltage characteristics for the studied HJs were measured within 280–300 K. The transport properties of the HJs are explained in terms of Anderson model with reference to aforementioned current transport models. It is found, that the mechanisms of current transport for all of the studied HJs are similar. At a low forward voltage bias the tunneling current dominates while at medium voltage bias (0.5–1 V) multitunneling capture-emission prevails with the electron trap located at 0.1–0.25 eV below the bottom of a ZnO (Zn1−xMgxO) conduction band. Beyond this voltage bias space charge limited current governs the current transport.

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Authors and Affiliations

E. Płaczek-Popko
K.M. Paradowska
M.A. Pietrzyk
A. Kozanecki
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Abstract

The Sianjo-anjo reservoir is used to meet the need for downstream clean water. Land activity at the Sianjo- anjo reservoir watershed can potentially increase the rate of erosion and the silting of rivers and reservoirs due to sedimentation. Reservoir siltation is a crucial challenge for reservoir management because it can reduce its function and affect its service life. However, sediment yield is often overlooked in reservoir planning and environmental assessment. This study aims to predict the rate of land erosion and sediment yield, and create an erosion hazard map of the Sianjo-anjo reservoir watershed. The study used a Geographic Information System, GIS-based Universal Soil Loss Equation (USLE) method and discovered that the erosion rate of the Sianjo-anjo reservoir watershed was between 35.23 Mg∙ha –1∙y –1 until 455.08 Mg∙ha –1∙y –1, with 95.85% classified as the low level, 0.03% as moderate, and 4.12% as high. Meanwhile, the sediment yield from the Sianjo-anjo reservoir watershed was 218,812.802 Mg∙y –1. USLE is vital to identify areas susceptible to erosion and crucial for reservoir sustainability. Furthermore, it is necessary to plan good sediment management. Long-term land conservation is required to maintain storage capacity and ensure effective operation of the reservoir.
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Authors and Affiliations

Felia Gusma
1
Azmeri Azmeri
1
ORCID: ORCID
Faris Z. Jemi
2
ORCID: ORCID
Hafnati Rahmatan
3
ORCID: ORCID

  1. Universitas Syiah Kuala, Engineering Faculty, Civil Engineering Department, Syech Abdur-Rauf No. 7 Darussalam, 23111, Banda Aceh, Indonesia
  2. Universitas Syiah Kuala, Engineering Faculty, Electrical Engineering Department, Banda Aceh, Indonesia
  3. Universitas Syiah Kuala, Faculty of Education and Teacher Training, Biology Department, Banda Aceh, Indonesia
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Abstract

Unlike many other countries, tropical regions such as Indonesia still lack publications on pedotransfer functions (PTFs), particularly ones dedicated to the predicting of soil bulk density. Soil bulk density affects soil density, porosity, water holding capacity, drainage, and the stock and flux of nutrients in the soil. However, obtaining access to a laboratory is difficult, time-consuming, and costly. Therefore, it is necessary to utilise PTFs to estimate soil bulk density. This study aims to define soil properties related to soil bulk density, develop new PTFs using multiple linear regression (MLR), and evaluate the performance and accuracy of PTFs (new and existing). Seven existing PTFs were applied in this study. For the purposes of evaluation, Pearson’s correlation (r), mean error (ME), root mean square error (RMSE), and modelling efficiency (EF) were used. The study was conducted in five soil types on Bintan Island, Indonesia. Soil depth and organic carbon (SOC) are soil properties potentially relevant for soil bulk density prediction. The ME, RMSE, and EF values were lower for the newly developed PTFs than for existing PTFs. In summary, we concluded that the newly developed PTFs have higher accuracy than existing PTFs derived from literature. The prediction of soil bulk density will be more accurate if PTFs are applied directly in the area that is to be studied.
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Authors and Affiliations

Evi Dwi Yanti
1
ORCID: ORCID
Asep Mulyono
1
ORCID: ORCID
Muhamad Rahman Djuwansah
1
ORCID: ORCID
Ida Narulita
1
ORCID: ORCID
Risandi Dwirama Putra
2
ORCID: ORCID
Dewi Surinati
3
ORCID: ORCID

  1. Research Center for Geotechnology, Indonesian National Research and Innovation Agency, Bandung, Indonesia
  2. Maritim Raja Ali Haji University, Tanjung Pinang, Indonesia
  3. Research Center for Oceanography, Indonesian National Research and Innovation Agency, Jakarta, Indonesia
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Abstract

The work concerns of modeling the process of manufacturing machine parts by casting method. Making a casting without internal defects is a difficult task and usually requires numerous computer simulations and their experimental verification at the prototyping stage. Numerical simulations are then of priority importance in determining the appropriate parameters of the casting process and in selecting the shape of the riser for the casting fed with it. These actions are aimed at leading shrinkage defects to the riser, so that the casting remains free from this type of defects. Since shrinkage defects usually disqualify the casting from its further use, this type of research is still valid and requires further work. The paper presents the mathematical model and the results of numerical simulations of the casting solidification process obtained by using the Finite Element Method (FEM). A partial differential equation describing the course of thermal phenomena in the process of 3D casting creating was applied. This equation was supplemented with appropriate boundary and initial conditions that define the physical problem under consideration. In numerical simulations, by selecting the appropriate shape riser, an attempt was made to obtain a casting without internal defects, using a simple method of identifying their location. This is the main aim of the research as such defects in the casting disqualify it from use.
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Authors and Affiliations

L. Sowa
1
ORCID: ORCID
T. Skrzypczak
1
ORCID: ORCID
P. Kwiatoń
1
ORCID: ORCID

  1. Czestochowa University of Technology, Department of Mechanics and Machine Design Fundamentals, Dąbrowskiego 73, 42-200 Częstochowa, Poland
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Abstract

The extinct arachnid order Trigonotarbida Petrunkevitch, 1949 is reported here for the first time from Ukraine. The material consists of an opisthosoma preserved in ventral view from the upper Carboniferous (lower Moscovian; Paralegoceras–Eowellerites ammonoid zone) of the Gorlivka locality in the Donets Basin, eastern Ukraine. Formal assignment to a family or genus is difficult, but the preserved ventral anatomy is consistent with a member of the families Aphantomartidae Petrunkevitch, 1945, Kreischeriidae Haase, 1890 or Eophrynidae Karsch, 1882. It is noteworthy for expanding the known distribution of trigonotarbids in Europe and is only the second Palaeozoic arachnid to be formally described from Ukraine; the other being the carapace of a whip scorpion (Thelyphonida Latreille, 1804) from Lomovatka in the Luhansk Region, also in the Donets Basin.
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Authors and Affiliations

Jason A. Dunlop
1
Vitaly S. Dernov
2

  1. Museum für Naturkunde, Leibniz Institute for Evolution and Biodiversity Science, Invalidenstrasse 43, D-10115 Berlin, Germany
  2. Institute of Geological Sciences, National Academy of Sciences of Ukraine, Oles Honchar Street 55b, 01054 Kyiv, Ukraine
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Abstract

A survey of breeding birds was carried out during the summer 1997-98 in several localities of the northern Danco Coast, Antarctic Peninsula. A total of 10 species were recorded: Pygoscelis antarctica (3234 pairs), P. papua (1888), Macronectes giganteus (76), Daption capense (61), Oceanites oceanicus (104), Phalacrocorax bransfieldensis (92), Ononis alba (15), Catharacta maccormicki (168), Lams dominicanus (583) and Sterna vittata (160 pairs).

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Authors and Affiliations

Marco Favero
Néstor Rubén Coria
Maria Paula Beron
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Abstract

This electronic paper presents an innovative technology for efficient use of the radio spectrum. This new frequency reconfigurable rotatable antenna is intended for wireless applications such as WLAN, WiMAX and Bluetooth mobile applications. The working principle of this proposed work is to print square patches mounted on the same circular dielectric substrate feed by a proximity coupling to eliminate the noise signal transmission and problems related to interference. The three positions correspond to an operating frequency controlled by a bipolar step-by-step engine. An optimization of the structure using the FEM finite element method as well as a comparison with other structures recently realized are detailed in this paper. The final numerical simulation results are: WLAN 4.95-5.53 GHz (BW = 11%) Gain = 6.06 dBi, WiMAX 3.35-3.75 GHz (BW = 11.2%) Gain = 7.48 dBi and Bluetooth 2.3-2.51 GHz (BW = 8.7%) Gain = 17.78 dBi.

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Authors and Affiliations

Aziz El Fatimi
Seddik Bri
Adil Saadi

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