Enhanced Thermionic Emission Cooling in High Barrier Superlattice Heterostructures

1998 ◽  
Vol 545 ◽  
Author(s):  
Ali Shakouri ◽  
Chris LaBounty ◽  
Patrick Abraham ◽  
Joachim Piprek ◽  
John E. Bowers
Keyword(s):  
Barrier Height ◽  
Thermoelectric Properties ◽  
Barrier Layer ◽  
Thermionic Emission ◽  
Experimental Results ◽  
Hot Electrons ◽  
Cooling Efficiency ◽  
Bulk Materials ◽  
Order Of Magnitude ◽  
Magnitude Improvement

AbstractThermionic emission current in heterostructures can be used to enhance thermoelectric properties beyond what can be achieved with conventional bulk materials. The Bandgap discontinuity at the junction between two materials is used to selectively emit hot electrons over a barrier layer from cathode to anode. This evaporative cooling can be optimized at various temperatures by adjusting the barrier height and thickness. Theoretical and experimental results for nonisothermal thermionic emission in heterostructures are presented. Single stage InGaAsP-based heterostructure integrated thermionic (HIT) coolers are fabricated and characterized. Cooling on the order of a degree over one micron thick barriers has been observed. Nonisothermal transport in highly doped tall barrier superlattices is also investigated. An order of magnitude improvement in cooling efficiency is predicted for InAlAs/InP superlattices.

A Method for Estimating and Compensating Quasistatic Errors of Machine Tools

1993 ◽  
Vol 115 (1) ◽  
pp. 149-159 ◽  
Author(s):  
P. M. Ferreira ◽  
C. Richard Liu
Keyword(s):  
Parameter Estimation ◽  
Error Compensation ◽  
Machine Tools ◽  
Experimental Results ◽  
Compensation Scheme ◽  
Order Of Magnitude ◽  
Magnitude Improvement

Quasistatic errors are the major contributors to positioning inaccuracies of machine tools. These errors, estimated to account for 70 percent of the errors of the machine, have been observed to be as high as 70 to 120 μm for production class machining centers. In this paper, a model for these errors is developed. Further, it is shown that the parameters for this model can be estimated by the observation of a few (nine) error vectors in the machine’s workspace. These two results form the basis for a viable error compensation scheme; the model for error compensation and the parameter estimation for updating the model. Experimental results verify the validity of the approach. An order-of-magnitude improvement in the accuracy of the machine, with respect to a calibration frame, was observed.

GaAs Devices for Low Loss Power Rectification

1992 ◽  
Vol 281 ◽  
Author(s):  
L. V. Munukutla ◽  
S. H. Cheng ◽  
S. J. Anderson
Keyword(s):  
Barrier Height ◽  
Vapor Phase ◽  
High Voltage ◽  
Experimental Results ◽  
Low Loss ◽  
Barrier Heights ◽  
Schottky Rectifiers ◽  
Gaas Devices ◽  
Order Of Magnitude ◽  
Good Agreement

ABSTRACTHigh voltage GaAs Schottky rectifiers fabricated using vapor phase epitaxy have been observed to be an order of magnitude higher in switching speeds than silicon. Measured rectifier barrier heights deduced from the I-V and C-V plots were found to be in good agreement with previously reported values. Our experimental results show no correlation between the epilayer thickness and barrier height.

Luminescence Properties of Europium-Doped Yttrium Oxides Derived from Their Dodecylsulfate-Templated Mesostructure and Nanotube Forms

2003 ◽  
Vol 775 ◽  
Author(s):  
Tsuyoshi Kijima ◽  
Kenichi Iwanaga ◽  
Tomomi Hamasuna ◽  
Shinji Mohri ◽  
Mitsunori Yada ◽  
...  
Keyword(s):  
Room Temperature ◽  
Broad Band ◽  
Concentration Quenching ◽  
Precipitation Method ◽  
Homogeneous Precipitation ◽  
Bulk Materials ◽  
Main Band ◽  
Homogeneous Precipitation Method ◽  
Order Of Magnitude ◽  
Weak Luminescence

AbstractEuropium-doped hexagonal-mesostructured and nanotubular yttrium oxides templated by dodecylsulfate species as well as surfactant free bulk oxides were synthesized by the homogeneous precipitation method. All the as grown nanostructured or bulk materials with amorphous or poorly crystalline frameworks showed weak luminescence bands at room temperature. On calcination at 1000°C these materials were converted into highly crystalline yttrium oxides, resulting in a total increase in intensity of all the bands by one order of magnitude. In the hexagonal-mesostructured system, the main band due to the 5D0-7F2 transition for the calcined phases showed a sharp but asymmetrical multiplet splitting indicating multiple Eu sites. Concentration quenching was found at a Eu content of 3 mol% or above for these phases. In contrast, the main emission for the calcined solids in the nanotubular system occurred as poorly resolved broad band and the intensity of the main band at higher Eu content was significantly enhanced compared with those for the other two systems.

High-Density Memristor-CMOS Ternary Logic Family

2020 ◽  
Author(s):  
Xiaoyuan Wang ◽  
Pengfei Zhou ◽  
Jason Eshraghian ◽  
Chih-Yang Lin ◽  
Herbert Ho-Ching Iu ◽  
...  
Keyword(s):  
Indium Tin Oxide ◽  
Practical Implementation ◽  
Switching Speed ◽  
High Data ◽  
Fast Switching ◽  
Data Density ◽  
Order Of Magnitude ◽  
High Transconductance ◽  
Logic Functions ◽  
Magnitude Improvement

<div>This paper presents the first experimental demonstration</div><div>of a ternary memristor-CMOS logic family. We systematically</div><div>design, simulate and experimentally verify the primitive</div><div>logic functions: the ternary AND, OR and NOT gates. These are then used to build combinational ternary NAND, NOR, XOR and XNOR gates, as well as data handling ternary MAX and MIN gates. Our simulations are performed using a 50-nm process which are verified with in-house fabricated indium-tin-oxide memristors, optimized for fast switching, high transconductance, and low current leakage. We obtain close to an order of magnitude improvement in data density over conventional CMOS logic, and a reduction of switching speed by a factor of 13 over prior state-of-the-art ternary memristor results. We anticipate extensions of this work can realize practical implementation where high data density is of critical importance.</div>

scholarly journals Incremental Construction of Generalized Voronoi Diagrams on Pointerless Quadtrees

2014 ◽  
Vol 2014 ◽  
pp. 1-14 ◽  
Author(s):  
Quanjun Yin ◽  
Long Qin ◽  
Xiaocheng Liu ◽  
Yabing Zha
Keyword(s):  
Voronoi Diagrams ◽  
Surrounding Area ◽  
Repair Mechanism ◽  
Local Repair ◽  
Order Of Magnitude ◽  
Generalized Voronoi Diagrams ◽  
Incremental Construction ◽  
Coarse To Fine ◽  
Multiple Granularities ◽  
Magnitude Improvement

In robotics, Generalized Voronoi Diagrams (GVDs) are widely used by mobile robots to represent the spatial topologies of their surrounding area. In this paper we consider the problem of constructing GVDs on discrete environments. Several algorithms that solve this problem exist in the literature, notably the Brushfire algorithm and its improved versions which possess local repair mechanism. However, when the area to be processed is very large or is of high resolution, the size of the metric matrices used by these algorithms to compute GVDs can be prohibitive. To address this issue, we propose an improvement on the current algorithms, using pointerless quadtrees in place of metric matrices to compute and maintain GVDs. Beyond the construction and reconstruction of a GVD, our algorithm further provides a method to approximate roadmaps in multiple granularities from the quadtree based GVD. Simulation tests in representative scenarios demonstrate that, compared with the current algorithms, our algorithm generally makes an order of magnitude improvement regarding memory cost when the area is larger than210×210. We also demonstrate the usefulness of the approximated roadmaps for coarse-to-fine pathfinding tasks.

Enhancing the Thermoelectric Properties in Carbon Fiber/Cement Composites by Using Steel Slag

2013 ◽  
Vol 539 ◽  
pp. 103-107 ◽  
Author(s):  
Jun Qing Zuo ◽  
Wu Yao ◽  
Jun Jie Qin
Keyword(s):  
Carbon Fiber ◽  
Linear Relationship ◽  
Thermoelectric Power ◽  
Thermoelectric Properties ◽  
Steel Slag ◽  
Experimental Results ◽  
Cement Composites ◽  
Temperature Differential ◽  
High Concentration ◽  
Good Linear

Thermoelectric properties of steel slag-carbon fiber/cement composites were studied in this paper. The effect of steel slag content on thermoelectric properties was focused on especially. The experimental results show that the addition of steel slag leads to an increase in the positive thermoelectric power of the cabon fiber/cement composites. The highest absolute thermoelectric power of carbon fiber/cement composites was rendered as positive as 14.4µV/°C by using steel slag, which had a high concentration of holes. Beside, a good linear relationship was observed between thermoelectric power and temperature differential on the specimen.

LOW TEMPERATURE THERMOELECTRIC PROPERTIES AND AGING PHENOMENA OF NANOSTRUCTURED p-TYPE Bi2-XSbXTe3 (x = 1.46, 1.48, 1.52 AND 1.55)

2013 ◽  
Vol 06 (05) ◽  
pp. 1340008 ◽  
Author(s):  
DALE HITCHCOCK ◽  
YEN-LIANG LIU ◽  
YUFEI LIU ◽  
TERRY M. TRITT ◽  
JIAN HE ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
Low Temperature ◽  
Thermoelectric Properties ◽  
Optimal Composition ◽  
Ambient Conditions ◽  
Bulk Materials ◽  
The Past ◽  
Aging Phenomena ◽  
P Type ◽  
Cold Pressed

Over the past decade the widely used p-type ( Bi 2-x Sb x) Te 3 bulk thermoelectric materials have been subject to various nanostructuring processes for higher thermoelectric performance. However, these nanostructuring processing were conducted on compositions optimized for bulk materials (x ~ 1.52–1.55). This leads to the question of whether the optimal composition for bulk materials is the same for their nanoscale counterparts. In this work we hydrothermally grew Bi 2-x Sb x Te 3 nanopowders (nominally, x = 1.46, 1.48, 1.52 and 1.55) and measured their thermoelectric properties on cold-pressed vacuum-sintered pellets (74–78% of the theoretical density) below 300 K. The measurements were conducted 18 months apart to probe the aging phenomena, with the samples stored in ambient conditions. We have found that (i) the peak of thermopower shifts to lower temperatures upon nanostructuring but it shifts back to higher temperatures upon aging; (ii) the electrical conductivity degrades by a factor of 1.5–2.3 upon aging while the temperature dependence is largely retained; and (iii) the ZT of freshly made samples is sensitive to the x value, a maximum ZT ~ 1.25(~ 0.62) at ~ 270 K (~ 255 K) was attained in the freshly made sample x = 1.55(x = 1.46), respectively; while the ZT of aged samples is significantly lowered by a factor of 2–4 but lesser x-dependent. These observations have been discussed in the context of charge buildup and compensation at grain boundaries.

scholarly journals Betweenness centrality profiles in trees

2017 ◽  
Vol 5 (5) ◽  
pp. 776-794
Author(s):  
Benjamin Fish ◽  
Rahul Kushwaha ◽  
György Turán
Keyword(s):  
Betweenness Centrality ◽  
Shortest Paths ◽  
Random Trees ◽  
Experimental Results ◽  
Basic Notion ◽  
Worst Case ◽  
Scale Free ◽  
Order Of Magnitude

Abstract Betweenness centrality of a vertex in a graph measures the fraction of shortest paths going through the vertex. This is a basic notion for determining the importance of a vertex in a network. The $k$-betweenness centrality of a vertex is defined similarly, but only considers shortest paths of length at most $k$. The sequence of $k$-betweenness centralities for all possible values of $k$ forms the betweenness centrality profile of a vertex. We study properties of betweenness centrality profiles in trees. We show that for scale-free random trees, for fixed $k$, the expectation of $k$-betweenness centrality strictly decreases as the index of the vertex increases. We also analyse worst-case properties of profiles in terms of the distance of profiles from being monotone, and the number of times pairs of profiles can cross. This is related to whether $k$-betweenness centrality, for small values of $k$, may be used instead of having to consider all shortest paths. Bounds are given that are optimal in order of magnitude. We also present some experimental results for scale-free random trees.

scholarly journals The Array of Long Baseline Antennas for Taking Radio Observations from the Sub-Antarctic

2020 ◽  
Vol 09 (04) ◽  
pp. 2050019
Author(s):  
H. C. Chiang ◽  
T. Dyson ◽  
E. Egan ◽  
S. Eyono ◽  
N. Ghazi ◽  
...  
Keyword(s):  
Low Frequency ◽  
Neutral Hydrogen ◽  
Radio Frequency Interference ◽  
Marion Island ◽  
Radio Observations ◽  
Long Baseline ◽  
Galactic Emission ◽  
Operating Frequency Range ◽  
Order Of Magnitude ◽  
Magnitude Improvement

Measurements of redshifted 21[Formula: see text]cm emission of neutral hydrogen at [Formula: see text][Formula: see text]MHz have the potential to probe the cosmic “dark ages,” a period of the universe’s history that remains unobserved to date. Observations at these frequencies are exceptionally challenging because of bright Galactic foregrounds, ionospheric contamination, and terrestrial radio-frequency interference. Very few sky maps exist at [Formula: see text][Formula: see text]MHz, and most have modest resolution. We introduce the Array of Long Baseline Antennas for Taking Radio Observations from the Sub-Antarctic (ALBATROS), a new experiment that aims to image low-frequency Galactic emission with an order-of-magnitude improvement in resolution over existing data. The ALBATROS array will consist of antenna stations that operate autonomously, each recording baseband data that will be interferometrically combined offline. The array will be installed on Marion Island and will ultimately comprise 10 stations, with an operating frequency range of 1.2–125[Formula: see text]MHz and maximum baseline lengths of [Formula: see text][Formula: see text]km. We present the ALBATROS instrument design and discuss pathfinder observations that were taken from Marion Island during 2018–2019.

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