2,283 research outputs found
Maintaining coherence in Quantum Computers
The effect of the inevitable coupling to external degrees of freedom of a
quantum computer are examined. It is found that for quantum calculations (in
which the maintenance of coherence over a large number of states is important),
not only must the coupling be small but the time taken in the quantum
calculation must be less than the thermal time scale, . For longer
times the condition on the strength of the coupling to the external world
becomes much more stringent.Comment: 13 page
Radiation Reaction fields for an accelerated dipole for scalar and electromagnetic radiation
The radiation reaction fields are calculated for an accelerated changing
dipole in scalar and electromagnetic radiation fields. The acceleration
reaction is shown to alter the damping of a time varying dipole in the EM case,
but not the scalar case. In the EM case, the dipole radiation reaction field
can exert a force on an accelerated monopole charge associated with the
accelerated dipole. The radiation reaction of an accelerated charge does not
exert a torque on an accelerated magnetic dipole, but an accelerated dipole
does exert a force on the charge. The technique used is that originally
developed by Penrose for non-singular fields and extended by the author for an
accelerated monopole charge.Comment: 11 page
Design and test of aircraft engine isolators for reduced interior noise
Improved engine vibration isolation was proposed to be the most weight and cost efficient retrofit structure-borne noise control measure for single engine general aviation aircraft. A study was carried out the objectives: (1) to develop an engine isolator design specification for reduced interior noise transmission, (2) select/design candidate isolators to meet a 15 dB noise reduction design goal, and (3) carry out a proof of concept evaluation test. Analytical model of the engine, vibration isolators and engine mount structure were coupled to an empirical model of the fuselage for noise transmission evaluation. The model was used to develop engine isolator dynamic properties design specification for reduced noise transmission. Candidate isolators ere chosen from available product literature and retrofit to a test aircraft. A laboratory based test procedure was then developed to simulate engine induced noise transmission in the aircraft for a proof of concept evaluation test. Three candidate isolator configurations were evaluated for reduced structure-borne noise transmission relative to the original equipment isolators
Engine isolation for structural-borne interior noise reduction in a general aviation aircraft
Engine vibration isolation for structural-borne interior noise reduction is investigated. A laboratory based test procedure to simulate engine induced structure-borne noise transmission, the testing of a range of candidate isolators for relative performance data, and the development of an analytical model of the transmission phenomena for isolator design evaluation are addressed. The isolator relative performance test data show that the elastomeric isolators do not appear to operate as single degree of freedom systems with respect to noise isolation. Noise isolation beyond 150 Hz levels off and begins to decrease somewhat above 600 Hz. Coupled analytical and empirical models were used to study the structure-borne noise transmission phenomena. Correlation of predicted results with measured data show that (1) the modeling procedures are reasonably accurate for isolator design evaluation, (2) the frequency dependent properties of the isolators must be included in the model if reasonably accurate noise prediction beyond 150 Hz is desired. The experimental and analytical studies were carried out in the frequency range from 10 Hz to 1000 Hz
Early history of the moon: Implications of U-Th-Pb and Rb-Sr systematics
Anorthosite 60015 contains the lowest initial Sr-87/Sr-86 ratio yet reported for a lunar sample. The initial ratio is equal to that of the achondrite Angra dos Reis and slightly higher than the lowest measured Sr-87/Sr-86 ratio for an inclusion in the C3 carbonaceous chondrite Allende. The Pb-Pb ages of both Angra does Reis and Allende are 4.62 X 10 to the ninth power yr. Thus, the initial Sr/87/Sr-86 ratio found in lunar anorthosite 60015 strongly supports the hypothesis that the age of the Moon is about 4.65 b.y. The U-238/Pb-204 value estimated for the source of the excess lead in "orange soil" 74220 is approximately 35 and lower than the values estimated for the sources of KREEP (600-1000), high-K (300-600), and low-K (100-300) basalts. From these and other physical, chemical and petrographic results it was hypothesized that (1) the moon formed approximately 4.65 b.y. ago; (2) a global-scale gravitational differentiation occurred at the beginning of lunar history; and (3) the differentiation resulted in a radical chemical and mineralogical zoning in which the U-238/Pb-204 ratios increased toward the surface, with the exception of the low U-238/Pb-204 surficial anorthositic layer which "floated" at the beginning of the differentiation relative to the denser pyroxene-rich material
Early history of the moon: Implications of U-Th-Pb and Rb-Sr systematics
Anorthosite 60015 contains the lowest initial Sr-87/Sr-86 ratio (0.69884 + or - 0.00004) yet reported for a lunar sample. The initial ratio is equal to that of the achondrite Angra dos Reis and slightly higher than the lowest measured Sr-87/Sr-86 ratio for an inclusion in the C3 carbonaceous chondrite Allende. The Pb-Pb ages of both Angra dos Reis and Allende are 4.62 x 10 to the 9th power years (4.62 billion years). Thus, the initial Sr-87/Sr-86 ratio found in lunar anorthosite 60015 strongly supports the hypothesis that the age of the moon is about 4.65 b.y. The U-238/Pb-204 value estimated for the source of the excess lead in orange soil 74220 is lower than the values estimated for the sources of KREEP (600-1000), high K (300-600) and low K (100-300) basalts
Engine-induced structural-borne noise in a general aviation aircraft
Structural borne interior noise in a single engine general aviation aircraft was studied to determine the importance of engine induced structural borne noise and to determine the necessary modeling requirements for the prediction of structural borne interior noise. Engine attached/detached ground test data show that engine induced structural borne noise is a primary interior noise source for the single engine test aircraft, cabin noise is highly influenced by responses at the propeller tone, and cabin acoustic resonances can influence overall noise levels. Results from structural and acoustic finite element coupled models of the test aircraft show that wall flexibility has a strong influence on fundamental cabin acoustic resonances, the lightweight fuselage structure has a high modal density, and finite element analysis procedures are appropriate for the prediction of structural borne noise
The ‘Evidentiary Bind’ in Postwar Land Restitution: The Case of Sri Lanka
The enormity of the world’s dislocated population generated by contemporary conflicts has brought significant attention to a complicated process of returning housing, land and property (HLP) to their rightful occupants once conditions permit. As the complexity of large-scale HLP restitution becomes increasingly apparent, significant obstacles emerge that require examination. This article describes how the ‘evidentiary bind’ is such an obstacle. This bind emerges when large-scale HLP restitution processes require titles and deeds to be in the possession of the population who are the least likely to have them—the forcibly displaced. The technical, legal and political inability to acknowledge and accept alternative, informal, customary, or hybrid evidence for finding rightful owners means that the ‘evidentiary bind’ prevents returns, leaves a large amount of land in a state of limbo, produces grievances in the war-affected population, and invites corruption and the use of potentially destabilizing means to regain one’s HLP. This article looks at the case of Sri Lanka where the current HLP restitution process faces a particularly acute form of the ‘evidentiary bind.
The Role of Land Conflict and Land Conflict Resolution in a Peace Process: Mozambique's Return to Agriculture
The massive return and reintegration of
refugees and displaced persons in Mozambique
(the largest in the histoy of
Africa) has pushed land tenure issues to
the fore in the county's peace process.
While land re-access for the six million
dislocatees is critical for food, security
and political stability, conflict over land
resources has become a primary concern
of the government and both the regional
and international community participating in Mozambique's recovery.
Based on data recently collected over a
year-and-a-half in Mozambique, this
paper will look at the problematic issues
of land access, land conflict, and land
conflict resolution emerging from the
recent 16 year war, and highlight the
role of organizations from the national
to the international, in land conflict
resolution.Le retour massif et la réintégration des
réfugiés et des personnes déplacées au
Mozambique (la plus vaste entreprise
de réintégration de toute l'histoire de
l'Afrique) a mis la question de la propriété
terrienne au centre du processus
de paix dans ce pays. Alors que l'accès
renouvelé à la terre apparaît crucial
pour les six millions de personnes
relocalisées pour des raisons alimentaires,
de sécurité, et de stabilité politique,
les conflits en matière de ressources
terriennes sont devenus la principale
inquiétude du gouvernement et des
communautés régionales et internationales
impliquées dans la reconstruction
du Mozambique. S'appuyant sur des
données colligées sur le terrain lors d'un
séjour d'un an et demi au Mozambique,
le présent article étudie la question problématique de l'accès à la terre, des contentieux
fonciers, et de leur résolution,
suite à la récente guerre de 16 ans. Sera
mis en relief le rôle des organisations
nationales et internationales dans la
résolution des contentieux fonciers
On the physical meaning of the Unruh effect
We present simple arguments that detectors moving with constant acceleration
(even acceleration for a finite time) should detect particles. The effect is
seen to be universal. Moreover, detectors undergoing linear acceleration and
uniform, circular motion both detect particles for the same physical reason. We
show that if one uses a circularly orbiting electron in a constant external
magnetic field as the Unruh--DeWitt detector, then the Unruh effect physically
coincides with the experimentally verified Sokolov--Ternov effect.Comment: 7 pages, 0 figures references added, small changes in text. To be
published JETP Lett
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