4,689 research outputs found
The FRB 121102 Host Is Atypical among Nearby Fast Radio Bursts
We search for host galaxy candidates of nearby fast radio bursts (FRBs), FRB 180729.J1316+55, FRB 171020, FRB 171213, FRB 180810.J1159+83, and FRB 180814.J0422+73 (the second repeating FRB). We compare the absolute magnitudes and the expected host dispersion measure DMhost of these candidates with that of the first repeating FRB, FRB 121102, as well as those of long gamma-ray bursts (LGRBs) and superluminous supernovae (SLSNe), the proposed progenitor systems of FRB 121102. We find that while the FRB 121102 host is consistent with those of LGRBs and SLSNe, the nearby FRB host candidates, at least for FRB 180729.J1316+55, FRB 171020, and FRB 180814.J0422+73, either have a smaller DMhost or are fainter than FRB 121102 host, as well as the hosts of LGRBs and SLSNe. In order to avoid the uncertainty in estimating DMhost due to the line-of-sight effect, we propose a galaxy-group-based method to estimate the electron density in the intergalactic regions, and hence, DMIGM. The result strengthens our conclusion. We conclude that the host galaxy of FRB 121102 is atypical, and LGRBs and SLSNe are likely not the progenitor systems of at least most nearby FRB sources. The recently reported two FRB hosts differ from the host of FRB 121102 and also the host candidates suggested in this paper. This is consistent with the conclusion of our paper and suggests that the FRB hosts are very diverse
Tribological Comparison of Materials
Thesis (Ph.D.) University of Alaska Fairbanks, 2004Approximately 600,000 total joint replacement surgeries are performed each year in the
United States. Current artificial joint implants are mainly metal-on-plastic. The synthetic
biomaterials undergo degradation through fatigue and corrosive wear from load-bearing and the
aqueous ionic environment of the human body. Deposits o f inorganic salts can scratch weight-bearing
surfaces, making artificial joints stiff and awkward. The excessive wear debris from
polyethylene leads to osteolysis and potential loosening of the prosthesis. The lifetime for well-designed
artificial joints is at most 10 to 15 years. A patient can usually have two total joint
replacements during her/his lifetime. Durability is limited by the body’s reaction to wear debris of
the artificial joints. Wear of the artificial joints should be reduced.
A focus of this thesis is the tribological performance of bearing materials for Total
Replacement Artificial Joints (TRAJ). An additional focus is the scaffolds for cell growth from
both a tissue engineering and tribological perspective. The tribological properties of materials
including Diam ond-like Carbon (DLC) coated materials were tested for TRAJ implants. The
DLC coatings are chemically inert, impervious to acid and saline media, and are mechanically
hard. Carbon-based materials are highly biocompatible. A new alternative to total joints
implantation is tissue engineering. Tissue engineering is the replacement of living tissue with
tissue that is designed and constructed to meet the needs of the individual patient. Cells were
cultured onto the artificial materials, including metals, ceramics, and polymers, and the frictional
properties of these materials were investigated to develop a synthetic alternative to orthopedic
transplants.
Results showed that DLC coated materials had low friction and wear, which are desirable
tribological properties for artificial joint material. Cells grew on some of the artificial matrix
materials, depending on the surface chemistry, wettability, morphology, microstructure etc. The
dry, lubricated, and cell culture friction tests showed that bovine serum albumin solution and
culture media performed as lubricants. Frictional properties varied. Glass and TR-2 (PET,
polyethylene terephthalate) showed good cell culture results and low friction. Both are suitable
materials, both as artificial joint implant coatings and as substrates for preparing total joint
implants via tissue engineering.Signature Page -- Title page -- Abstract -- Table of Contents -- List of Figures -- List of Tables xiii
List of Appendices -- Acknowledgements -- Chapter 1: Introduction -- Chapter 2: Experimental: materials, equipment, and methods -- Chapter 3: Tribological performance of alternative bearing materials for TRAJ: results and discussion -- Chapter 3: Tribological performance of materials as scaffolds for cell growth:
Results and discussion of cell culture - a tissue engineering approach -- Chapter 4: Tribological performance of materials as scaffolds for cell growth:
Results and discussion of cell culture - a tissue engineering approach -- Chapter 5: Tribological performance of materials as scaffolds for cell growth:
Results and discussion of tribological tests -- Chapter 6: Conclusions and future work -- Reference -- Appendice
Electro-Thermal Codesign in Liquid Cooled 3D ICs: Pushing the Power-Performance Limits
The performance improvement of today's computer systems is usually accompanied by increased chip power consumption and system temperature. Modern CPUs dissipate an average of 70-100W power while spatial and temporal power variations result in hotspots with even higher power density (up to 300W/cm^2). The coming years will continue to witness a significant increase in CPU power dissipation due to advanced multi-core architectures and 3D integration technologies. Nowadays the problems of increased chip power density, leakage power and system temperatures have become major obstacles for further improvement in chip performance. The conventional air cooling based heat sink has been proved to be insufficient for three dimensional integrated circuits (3D-ICs). Hence better cooling solutions are necessary. Micro-fluidic cooling, which integrates micro-channel heat sinks into silicon substrates of the chip and uses liquid flow to remove heat inside the chip, is an effective active cooling scheme for 3D-ICs. While the micro-fluidic cooling provides excellent cooling to 3D-ICs, the associated overhead (cooling power consumed by the pump to inject the coolant through micro-channels) is significant. Moreover, the 3D-IC structure also imposes constraints on micro-channel locations (basically resource conflict with through-silicon-vias TSVs or other structures).
In this work, we investigate optimized micro-channel configurations that address the aforementioned considerations. We develop three micro-channel structures (hotspot optimized cooling configuration, bended micro-channel and hybrid cooling network) that can provide sufficient cooling to 3D-IC with minimum cooling power overhead, while at the same time, compatible with the existing electrical structure such as TSVs. These configurations can achieve up to 70% cooling power savings compared with the configuration without any optimization. Based on these configurations, we then develop a micro-fluidic cooling based dynamic thermal management approach that maintains the chip temperature through controlling the fluid flow rate (pressure drop) through micro-channels. These cooling configurations are designed after the electrical parts, and therefore, compatible with the current standard IC design flow.
Furthermore, the electrical, thermal, cooling and mechanical aspects of 3D-IC are interdependent. Hence the conventional design flow that designs the cooling configuration after electrical aspect is finished will result in inefficiencies. In order to overcome this problem, we then investigate electrical-thermal co-design methodology for 3D-ICs. Two co-design problems are explored: TSV assignment and micro-channel placement co-design, and gate sizing and fluidic cooling co-design. The experimental results show that the co-design enables a fundamental power-performance improvement over the conventional design flow which separates the electrical and cooling design. For example, the gate sizing and fluidic cooling co-design achieves 12% power savings under the same circuit timing constraint and 16% circuit speedup under the same power budget
Controlling quantum state transfer in spin chain with the confined field
As a demonstration of the spectrum-parity matching condition (SPMC) for
quantum state transfer, we investigate the propagation of single-magnon state
in the Heisenberg chain in the confined external tangent magnetic field
analytically and numerically. It shows that the initial Gaussian wave packet
can be retrieved at the counterpart location near-perfectly over a longer
distance if the dispersion relation of the system meets the SPMC approximately.Comment: 9 pages, 8 figure
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