5,085 research outputs found
Effective Management of an Image Collection in the Small Museum: Cataloging Storing Digitizing Images and the Impact of Digitization on the Museum and the Collection
Soil erosion evaluation in a small watershed in Brazil through 137 Cs fallout redistribution analysis and conventional models
An investigation of rates and patterns of soil erosion on agricultural land cultivated with sugarcane was undert a ken using the 137Cs technique, USLE (Universal Soil Loss Equation) and WEPP (Water Erosion Prediction Project) model. The study was carried out on a representative catchment of a small watershed of the Piracicaba river basin, State of São Paulo, Brazil, called Ceveiro watershed, well known for its severe soil degradation caused by erosion. The results from the 137Cs technique indicate that most part of the studied area (94%) are eroded at erosion rates that go up to 59 Mg ha-1 y-1, with a weighted average rate of 23 Mg ha-1 y-1 . The weighted average rate of infield deposition and sediment retrieval that occurs in only 6% of the total area was estimated to be around 12 Mg ha-1 y-1 . These values led to very high net soil loss from the field, with rates of the order of 21 Mg ha-1 y-1 , which represents a sediment delive ry ratio of 97%. A linear correlation between soil erosion rate estimated by the 137Cs technique and the amount of available K in the top soil layer (0-20 cm) was observed. Based on this correlation the estimated amounts of net and gross K loss in the grid area due to soil erosion were of 0.2 and 1.52 kg ha-1 y-1, respectively. The erosion rate estimated by USLE was 39 Mg ha-1 y-1 and by WEPP model 16.5 Mg ha-1 y-1 with a sediment delivery of 12.4 Mg ha-1 y-1 (75%). The results are a confirmation that the soil conservation practices adopted in the area are very poor and can explain the high siltation level of water reservoirs in the watershed
The "MyMobile" Handbook. Guidelines and scenarios formobile learning in adult education
Voltage control of magnetocrystalline anisotropy in ferromagnetic - semiconductor/piezoelectric hybrid structures
We demonstrate dynamic voltage control of the magnetic anisotropy of a
(Ga,Mn)As device bonded to a piezoelectric transducer. The application of a
uniaxial strain leads to a large reorientation of the magnetic easy axis which
is detected by measuring longitudinal and transverse anisotropic
magnetoresistance coefficients. Calculations based on the mean-field
kinetic-exchange model of (Ga,Mn)As provide microscopic understanding of the
measured effect. Electrically induced magnetization switching and detection of
unconventional crystalline components of the anisotropic magnetoresistance are
presented, illustrating the generic utility of the piezo voltage control to
provide new device functionalities and in the research of micromagnetic and
magnetotransport phenomena in diluted magnetic semiconductors.Comment: Submitted to Physical Review Letters. Updates version 1 to include a
more detailed discussion of the effect of strain on the anisotropic
magnetoresistanc
Lithographically and electrically controlled strain effects on anisotropic magnetoresistance in (Ga,Mn)As
It has been demonstrated that magnetocrystalline anisotropies in (Ga,Mn)As
are sensitive to lattice strains as small as 10^-4 and that strain can be
controlled by lattice parameter engineering during growth, through post growth
lithography, and electrically by bonding the (Ga,Mn)As sample to a
piezoelectric transducer. In this work we show that analogous effects are
observed in crystalline components of the anisotropic magnetoresistance (AMR).
Lithographically or electrically induced strain variations can produce
crystalline AMR components which are larger than the crystalline AMR and a
significant fraction of the total AMR of the unprocessed (Ga,Mn)As material. In
these experiments we also observe new higher order terms in the
phenomenological AMR expressions and find that strain variation effects can
play important role in the micromagnetic and magnetotransport characteristics
of (Ga,Mn)As lateral nanoconstrictions.Comment: 11 pages, 4 figures, references fixe
Soil erosion evaluation in a small watershed in Brazil through 137 Cs fallout redistribution analysis and conventional models
An investigation of rates and patterns of soil erosion on agricultural land cultivated with sugarcane was undert a ken using the 137Cs technique, USLE (Universal Soil Loss Equation) and WEPP (Water Erosion Prediction Project) model. The study was carried out on a representative catchment of a small watershed of the Piracicaba river basin, State of São Paulo, Brazil, called Ceveiro watershed, well known for its severe soil degradation caused by erosion. The results from the 137Cs technique indicate that most part of the studied area (94%) are eroded at erosion rates that go up to 59 Mg ha-1 y-1, with a weighted average rate of 23 Mg ha-1 y-1 . The weighted average rate of infield deposition and sediment retrieval that occurs in only 6% of the total area was estimated to be around 12 Mg ha-1 y-1 . These values led to very high net soil loss from the field, with rates of the order of 21 Mg ha-1 y-1 , which represents a sediment delive ry ratio of 97%. A linear correlation between soil erosion rate estimated by the 137Cs technique and the amount of available K in the top soil layer (0-20 cm) was observed. Based on this correlation the estimated amounts of net and gross K loss in the grid area due to soil erosion were of 0.2 and 1.52 kg ha-1 y-1, respectively. The erosion rate estimated by USLE was 39 Mg ha-1 y-1 and by WEPP model 16.5 Mg ha-1 y-1 with a sediment delivery of 12.4 Mg ha-1 y-1 (75%). The results are a confirmation that the soil conservation practices adopted in the area are very poor and can explain the high siltation level of water reservoirs in the watershed
EFFECTS OF RECLAIMED ASPHALT, WAX ADDITIVE, AND COMPACTION TEMPERATURE ON CHARACTERISTICS AND MECHANICAL PROPERTIES OF POROUS ASPHALT
This paper describes physical and mechanical properties of porous asphalt mixtures with various RAP amount (0%, 10%, 20%, 30%) containing one WMA additive (organic wax). The samples were prepared using the Marshall compactor at two different temperatures (125 °C, 145 °C) by fabricating six series of porous mixtures. Air void content, particle loss, stiffness modulus, indirect tensile strength, and indirect tensile strength ratio were measured and the effects of RAP, wax, and compaction temperatures were evaluated, considering the results of statistical analyses. Based on the performed tests, it has been concluded that high RAP contents (30%) in WMA-RAP PAs result in decreased porosity, permeability, and moisture resistance, and in increased cohesiveness, stiffness, and indirect tensile strength compared to the reference PAs. On the other hand, for low RAP contents (10%), WMA-RAP PAs show lower cohesiveness and indirect tensile strength, at the same time demonstrating an increase in porosity, permeability, moisture resistance, and stiffness. Reduced compaction temperatures (125 °C) particularly affect the cracking resistance
Experimental observation of the optical spin transfer torque
The spin transfer torque is a phenomenon in which angular momentum of a spin
polarized electrical current entering a ferromagnet is transferred to the
magnetization. The effect has opened a new research field of electrically
driven magnetization dynamics in magnetic nanostructures and plays an important
role in the development of a new generation of memory devices and tunable
oscillators. Optical excitations of magnetic systems by laser pulses have been
a separate research field whose aim is to explore magnetization dynamics at
short time scales and enable ultrafast spintronic devices. We report the
experimental observation of the optical spin transfer torque, predicted
theoretically several years ago building the bridge between these two fields of
spintronics research. In a pump-and-probe optical experiment we measure
coherent spin precession in a (Ga,Mn)As ferromagnetic semiconductor excited by
circularly polarized laser pulses. During the pump pulse, the spin angular
momentum of photo-carriers generated by the absorbed light is transferred to
the collective magnetization of the ferromagnet. We interpret the observed
optical spin transfer torque and the magnetization precession it triggers on a
quantitative microscopic level. Bringing the spin transfer physics into optics
introduces a fundamentally distinct mechanism from the previously reported
thermal and non-thermal laser excitations of magnets. Bringing optics into the
field of spin transfer torques decreases by several orders of magnitude the
timescales at which these phenomena are explored and utilized.Comment: 11 pages, 4 figure
The GBT-SCA, a radiation tolerant ASIC for detector control applications in SLHC experiments
This work describes the architecture of the GigaBit Transceiver – Slow Control Adapter (GBT–SCA) ASIC suitable for the control and monitoring applications of the embedded front-end electronics in the future SLHC experiments. The GBT–SCA is part the GBT chipset currently under development for the SLHC detector upgrades. It is designed for radiation tolerance and it will be fabricated in a commercial 130 nm CMOS technology. The paper discusses the GBT-SCA architecture, the data transfer protocol, the ASIC interfaces, and its integration with the GBT optical link. The GBT–SCA is one the components of the GBT system chipset. It is proposed for the future SLHC experiments and is designed to be configurable matching different front-end system requirements. The GBT-SCA is intended for the slow control and monitoring of the embedded front end electronics and implements a point-to-multi point connection between one GBT optical link ASIC and several front end ASICs. The GBT-SCA connects to a dedicated electrical port on the GBT ASIC that provides 80 Mbps of bidirectional data traffic. If needed, more than one GBT-SCA ASIC can be connected to a GBT ASIC thus increasing the control and monitoring capabilities in the system. The GBT-SCA ASIC features several I/O ports to interface with the embedded front-end ASICs. There are 16 I2C buses, 1 JTAG controller port, 4 8- bit wide parallel-ports, a memory bus controller and an ADC to monitor up to 8 external analog signals. All these ports are accessible from the counting room electronics, via the GBT optical link system. Special design techniques are being employed to protect the operation of the GBT-SCA against radiation induced Single-Event-Upsets to a level that is compatible for the SLHC experiments. The paper will present the overall architecture of the GBTSCA ASIC describing in detail the design of the peripheral controllers for the individual I/O ports, the network controller that implements the connectivity with the GBT ASIC and will discuss the operation modes and the flow of information between the control electronics and the embedded front end ASICs
Optimal low-thrust trajectories to asteroids through an algorithm based on differential dynamic programming
In this paper an optimisation algorithm based on Differential Dynamic Programming is applied to the design of rendezvous and fly-by trajectories to near Earth objects. Differential dynamic programming is a successive approximation technique that computes a feedback control law in correspondence of a fixed number of decision times. In this way the high dimensional problem characteristic of low-thrust optimisation is reduced into a series of small dimensional problems. The proposed method exploits the stage-wise approach to incorporate an adaptive refinement of the discretisation mesh within the optimisation process. A particular interpolation technique was used to preserve the feedback nature of the control law, thus improving robustness against some approximation errors introduced during the adaptation process. The algorithm implements global variations of the control law, which ensure a further increase in robustness. The results presented show how the proposed approach is capable of fully exploiting the multi-body dynamics of the problem; in fact, in one of the study cases, a fly-by of the Earth is scheduled, which was not included in the first guess solution
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