4,461 research outputs found
Feasibility and Performance of the Microwave Thermal Rocket Launcher
Beamed-energy launch concepts employing a microwave thermal thruster are feasible in principle, and microwave sources of sufficient power to launch tons into LEO already exist. Microwave thermal thrusters operate on an analogous principle to nuclear thermal thrusters, which have experimentally demonstrated specific impulses exceeding 850 seconds. Assuming such performance, simple application of the rocket equation suggests that payload fractions of 10% are possible for a single stage to orbit (SSTO) microwave thermal rocket. We present an SSTO concept employing a scaled X-33 aeroshell. The flat aeroshell underside is covered by a thin-layer microwave absorbent heat-exchanger that forms part of the thruster. During ascent, the heat-exchanger faces the microwave beam. A simple ascent trajectory analysis incorporating X-33 aerodynamic data predicts a 10% payload fraction for a 1 ton craft of this type. In contrast, the Saturn V had 3 non-reusable stages and achieved a payload fraction of 4%
The Microwave Thermal Thruster Concept
The microwave thermal thruster heats propellant via a heat-exchanger then expands it through a rocket nozzle to produce thrust. The heat-exchanger is simply a microwave-absorbent structure through which propellant flows in small channels. Nuclear thermal thrusters are based on an analogous principle, using neutrons rather than microwaves, and have experimentally demonstrated specific impulses exceeding 850 seconds. A microwave equivalent will likely have a similar specific impulse, since both nuclear and microwave thermal thrusters are ultimately constrained by material thermal limits, rather than the energy-density limits of chemical propellants. We present the microwave thermal thruster concept by characterizing a novel variation for beamed-energy launch. In reducing the thruster concept to practice, the enabling physical process is microwave absorption by refractory materials, and we examine semiconductor and susceptor-based approaches to achieving this absorption within the heat-exchanger structure
Groundwater reinjection and heat dissipation: lessons from the operation of a large groundwater cooling system in Central London
The performance of a large open-loop groundwater cooling scheme in a shallow alluvial aquifer at a prominent public building in Central London has been monitored closely over its first 2âyears of operation. The installed system provided cooling to the site continuously for a period of 9âmonths between June 2012 and April 2013. During this period, c. 131300âm3 of groundwater was abstracted from a single pumping well and recharged into a single injection borehole. The amount of heat rejected in this period amounts to c. 1.37âGWh. A programme of hydraulic testing was subsequently undertaken over a 3âmonth period between July and October 2013 to evaluate the performance of the injection borehole. The data indicate no significant change in injection performance between commissioning trials undertaken in 2010 and the most recent period of testing, as evidenced by comparison of injection pressures for given flow rates in 2010 and 2013. Continuous temperature monitoring of the abstracted water, the discharge and a number of observation wells demonstrates the evolution of a heat plume in the aquifer in response to heat rejection and subsequent dissipation of this heat during the 18âmonth planned cessation
When does the influence of maturation on anthropometric and physical fitness characteristics increase and subside?
The relationships between maturation and anthropometric and physical performance characteristics are dynamic and often asynchronous; confounding the capability to accurately evaluate performance during adolescence. This study aimed to (i) examine the influence of chronological age (CA) and somatic maturation (YPHV) upon anthropometric and physical performance parameters, and (ii) identify the transition/change time points in these relationships using segmental regression. N = 969 soccer players (8-18 years of age) completed anthropometric and physical test assessments, including a countermovement jump (CMJ), agility T test, 10 and 20 m sprints, and multistage fitness test (MSFT). When modeled against CA and YPHV, results identified time point phases with increased rates of stature (CA-7.5, YPHV-8.6 cm/y at 10.7-15.2 years or -3.2 to +0.8 YPHV) and body mass gain (CA-7.1, YPHV-7.5 kg/y at 11.9-16.1 years or -1.6 to +4.0 YPHV), followed by gain reductions. Increased rates of sprint performance development (31%-43% gains) occurred at 11.8-15.8 CA or -1.8 to +1.2 YPHV, with gains subsiding thereafter. CMJ, T test, and MSFT gains appeared relatively linear with no change in developmental rate apparent. Developmental tempos did again, however, subside at circa (CMJ and T test) to post-PHV (MSFT). Based on our sample and analysis, periods of increased developmental rates (stature, mass, sprint) were apparent alongside progressive gains for other physical measures, before all subsided at particular age and maturation time points. Findings highlight dynamic asynchronous development of players, physical attributes, and the need to account for the influence of maturation on athletic performance until post-PHV
Non-Fermi-liquid behavior in nearly ferromagnetic metallic SrIrO3 single crystals
We report transport and thermodynamic properties of single-crystal SrIrO3 as
a function of temperature T and applied magnetic field H. We find that SrIrO3
is a non-Fermi-liquid metal near a ferromagnetic instability, as characterized
by the following properties: (1) small ordered moment but no evidence for
long-range order down to 1.7 K; (2) strongly enhanced magnetic susceptibility
that diverges as T or T1/2 at low temperatures, depending on the applied field;
(3) heat capacity C(T,H) ~ -Tlog T that is readily amplified by low applied
fields; (4) a strikingly large Wilson ratio at T< 4K; and (5) a T3/2-dependence
of electrical resistivity over the range 1.7 < T < 120 K. A phase diagram based
on the data implies SrIrO3 is a rare example of a stoichiometric oxide compound
that exhibits non-Fermi-liquid behavior near a quantum critical point (T = 0
and H = 0.23 T)
Pressure-Induced Insulating State in Ba1-xRExIrO3 (RE = Gd, Eu) Single Crystals
BaIrO3 is a novel insulator with coexistent weak ferromagnetism, charge and
spin density wave. Dilute RE doping for Ba induces a metallic state, whereas
application of modest pressure readily restores an insulating state
characterized by a three-order-of-magnitude increase of resistivity. Since
pressure generally increases orbital overlap and broadens energy bands, a
pressure-induced insulating state is not commonplace. The profoundly dissimilar
responses of the ground state to light doping and low hydrostatic pressures
signal an unusual, delicate interplay between structural and electronic degrees
of freedom in BaIrO3
Non-uniform doping across the Fermi surface of NbS intercalates
Magnetic ordering of the first row transition metal intercalates of NbS
due to coupling between the conduction electrons and the intercalated ions has
been explained in terms of Fermi surface nesting. We use angle-resolved
photoelectron spectroscopy to investigate the Fermi surface topology and the
valence band structure of the quasi-two-dimensional layer compounds
MnNbS and NiNbS. Charge transfer from the intercalant
species to the host layer leads to non-uniform, pocket selective doping of the
Fermi surface. The implication of our results on the nesting properties are
discussed
Icemaker^(TM): an excel-based environment for collaborative design
The creative process of team design can be rapid and powerful when focused, yet complex designs, such as
spacecrafit, can slow and quench the essential elements
of this process. Concurrent Engineering techniques partially address this problem, but a fuller realization
of their benefits require an approach centering on
the human aspects of teamwork. ICEMaker^(TM)
is a Microsoft ExcelÂź based software tool that
facilitates closer-to-ideal collaboration within teams employing the new Integrated Concurrent Engineering
(ICE) methodology. ICE is a generic approach that emphasizes focused collaborative design in a single-room context, and is now employed at several aerospace organizations to increase the productivity of design teams
defining complex early development-phase products. By
way of introduction, this paper describes the basic elements
of ICE needed to understand ICEMaker and its application.
We present the design approach, philosophy, and client-server architecture of the ICEMaker system, as well as a
simplified user scenario. NASA's Jet Propulsion Laboratory
(JPL) has recently adopted ICEMaker for its primary early-phase space mission and system advanced project design team, Team-X. We describe Team-X's experience with
ICEMaker and report on the lessons learned, and qualitative
product improvements, resulting from JPL's implementation
of ICEMaker
The in situ synthesis of PbS nanocrystals from lead(II) n -octylxanthate within a 1,3-diisopropenylbenzeneâbisphenol A dimethacrylate sulfur copolymer
The synthesis of lead sulfide nanocrystals within a solution processable sulfur âinverse vulcanizationâ polymer thin film matrix was achieved from the in situ thermal decomposition of lead(II) n-octylxanthate, [Pb(S2COOct)2]. The growth of nanocrystals within polymer thin films from single-source precursors offers a faster route to networks of nanocrystals within polymers when compared with ex situ routes. The âinverse vulcanizationâ sulfur polymer described herein contains a hybrid linker system which demonstrates high solubility in organic solvents, allowing solution processing of the sulfur-based polymer, ideal for the formation of thin films. The process of nanocrystal synthesis within sulfur films was optimized by observing nanocrystal formation by X-ray photoelectron spectroscopy and X-ray diffraction. Examination of the film morphology by scanning electron microscopy showed that beyond a certain precursor concentration the nanocrystals formed were not only within the film but also on the surface suggesting a loading limit within the polymer. We envisage this material could be used as the basis of a new generation of materials where solution processed sulfur polymers act as an alternative to traditional polymers
The Anatomy of Sartorius Muscle and its Implications for Sarcoma Radiotherapy
Purpose: Controversy exists as to whether sartorius muscle is completely invested in fascia. If it is, then direct tumour
involvement from soft tissue sarcoma of the anterior thigh would be unlikely and would justify omitting sartorius from the
radiotherapy volume
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