375 research outputs found
How does a quadratic term in the energy dispersion modify the single-particle Green's function of the Tomonaga-Luttinger model?
We calculate the effect of a quadratic term in the energy dispersion on the
low-energy behavior of the Green's function of the spinless Tomonaga-Luttinger
model (TLM). Assuming that for small wave-vectors q = k - k_F the fermionic
excitation energy relative to the Fermi energy is v_F q + q^2 / (2m), we
explicitly calculate the single-particle Green's function for finite but small
values of lambda = q_c /(2k_F). Here k_F is the Fermi wave-vector, q_c is the
maximal momentum transfered by the interaction, and v_F = k_F / m is the Fermi
velocity. Assuming equal forward scattering couplings g_2 = g_4, we find that
the dominant effect of the quadratic term in the energy dispersion is a
renormalization of the anomalous dimension. In particular, at weak coupling the
anomalous dimension is tilde{gamma} = gamma (1 - 2 lambda^2 gamma), where gamma
is the anomalous dimension of the TLM. We also show how to treat the change of
the chemical potential due to the interactions within the functional
bosonization approach in arbitrary dimensions.Comment: 17 pages, 1 figur
A radiological assessment of nuclear power and propulsion operations near Space Station Freedom
Scenarios were identified which involve the use of nuclear power systems in the vicinity of Space Station Freedom (SSF) and their radiological impact on the SSF crew was quantified. Several of the developed scenarios relate to the use of SSF as an evolutionary transportation node for lunar and Mars missions. In particular, radiation doses delivered to SSF crew were calculated for both the launch and subsequent return of a Nuclear Electric Propulsion (NEP) cargo vehicle and a Nuclear Thermal Rocket (NTR) personnel vehicle to low earth orbit. The use of nuclear power on co-orbiting platforms and the storage and handling issues associated with radioisotope power systems were also explored as they relate to SSF. A central philosophy in these analyses was the utilization of a radiation dose budget, defined as the difference between recommended dose limits from all radiation sources and estimated doses received by crew members from natural space radiations. Consequently, for each scenario examined, the dose budget concept was used to identify and quantify constraints on operational parameters such as launch separation distances, returned vehicle parking distances, and reactor shutdown times prior to vehicle approach. The results indicate that realistic scenarios do not exist which would preclude the use of nuclear power sources in the vicinity of SSF. The radiation dose to the SSF crew can be maintained at safe levels solely by implementing proper and reasonable operating procedures
State of the States 2008: Renewable Energy Development and the Role of Policy
This report provides insights into the status of renewable energy development at the state level. Renewable resources are increasing in development overall, but state development varies by resource and rates of change. The factors contributing to renewable energy development at the state level are identified and discussed, including the challenges of understanding the role of different factors in development. The report also compiles and evaluates the status of 'best practice' state policy design and connects the existence of some policies with increased renewable energy development through correlation analysis. The report also proposes a strategy for better understanding the role of policy in renewable energy development, based on market-transformation principles. Correlation analysis illustrates the potential for further application of these principles to renewable energy. The final section provides resources for state policy makers for better understanding and developing renewable energy resources
Dynamic structure factor of Luttinger liquids with quadratic energy dispersion and long-range interactions
We calculate the dynamic structure factor S (omega, q) of spinless fermions
in one dimension with quadratic energy dispersion k^2/2m and long range
density-density interaction whose Fourier transform f_q is dominated by small
momentum-transfers q << q_0 << k_F. Here q_0 is a momentum-transfer cutoff and
k_F is the Fermi momentum. Using functional bosonization and the known
properties of symmetrized closed fermion loops, we obtain an expansion of the
inverse irreducible polarization to second order in the small parameter q_0 /
k_F. In contrast to perturbation theory based on conventional bosonization, our
functional bosonization approach is not plagued by mass-shell singularities.
For interactions which can be expanded as f_q = f_0 + f_0^{2} q^2/2 + O (q^4)
with finite f_0^{2} we show that the momentum scale q_c = 1/ | m f_0^{2} |
separates two regimes characterized by a different q-dependence of the width
gamma_q of the collective zero sound mode and other features of S (omega, q).
For q_c << q << k_F we find that the line-shape in this regime is
non-Lorentzian with an overall width gamma_q of order q^3/(m q_c) and a
threshold singularity at the lower edge.Comment: 33 Revtex pages, 17 figure
Dynamic scaling in the vicinity of the Luttinger liquid fixed point
We calculate the single-particle spectral function A (k, omega) of a
one-dimensional Luttinger liquid by means of a functional renormalization group
(RG) approach. Given an infrared energy cutoff Lambda = Lambda_0 e^{- l}, our
approach yields the spectral function in the scaling form, A_{\Lambda} (k_F +
p, omega) = tau Z_l tilde{A}_l (p xi, omega tau), where k_F is the Fermi
momentum, Z_l is the wave-function renormalization factor, tau = 1 / \Lambda is
the time scale and xi = v_F / \Lambda is the length scale associated with
Lambda. At the Luttinger liquid fixed point (l rightarrow infty) our RG result
for A (k, omega) exhibits the correct anomalous scaling properties, and for k =
\pm k_F agrees exactly with the well-known bosonization result at weak
coupling. Our calculation demonstrates that the field rescaling is essential
for obtaining the crossover from Fermi liquid behavior to Luttinger liquid
behavior from a truncation of the hierarchy of exact RG flow equations as the
infrared cutoff is reduced.Comment: 15 pages, 5 figure
Probabilistic seismic hazard map for Bulgaria as a basis for a new building code
A seismic hazard map proposed as part of a new building code for Bulgaria is presented here on basis of the recommendations in EUROCODE 8. <P> Seismic source zones within an area of about 200 km around Bulgaria were constructed considering seismicity, neotectonic and geological development. The most time consuming work was to establish a homogeneous earthquake catalogue out of different catalogues. <P> The probabilistic seismic hazard assessment in terms of intensities is performed following Cornell (1968) with the program EQRISK (see McGuire, 1976), modified by us for use of intensities. To cope with the irregular isoseismals of the Vrancea intermediate depth earthquakes a special attenuation factor is introduced (Ardeleanu et al., 2005), using detailed macroseismic maps of three major earthquakes. <P> The final seismic hazard is the combination of both contributions, of zones with crustal earthquakes and of the Vrancea intermediate depth earthquakes zone. Calculations are done for recurrence periods of 95, 475 and 10 000 years
Ferromagnetic Luttinger Liquids
We study weak itinerant ferromagnetism in one-dimensional Fermi systems using
perturbation theory and bosonization. We find that longitudinal spin
fluctuations propagate ballistically with velocity v_m << v_F, where v_F is the
Fermi velocity. This leads to a large anomalous dimension in the spin-channel
and strong algebraic singularities in the single-particle spectral function and
in the transverse structure factor for momentum transfers q ~ 2 Delta/v_F,
where 2 Delta is the exchange splitting.Comment: 4 pages, 3 figure
Radiative Transfer in Obliquely Illuminated Accretion Disks
The illumination of an accretion disk around a black hole or neutron star by
the central compact object or the disk itself often determines its spectrum,
stability, and dynamics. The transport of radiation within the disk is in
general a multi-dimensional, non-axisymmetric problem, which is challenging to
solve. Here, I present a method of decomposing the radiative transfer equation
that describes absorption, emission, and Compton scattering in an obliquely
illuminated disk into a set of four one-dimensional transfer equations. I show
that the exact calculation of the ionization balance and radiation heating of
the accretion disk requires the solution of only one of the one-dimensional
equations, which can be solved using existing numerical methods. I present a
variant of the Feautrier method for solving the full set of equations, which
accounts for the fact that the scattering kernels in the individual transfer
equations are not forward-backward symmetric. I then apply this method in
calculating the albedo of a cold, geometrically thin accretion disk.Comment: 16 pages, 3 figures; to appear in The Astrophysical Journa
Aktualisierung der Empfehlungen zur standardisierten Diagnostik und Klassifikation von Kaumuskel- und Kiefergelenkschmerzen
Zusammenfassung: Hintergrund: Im Jahre 2000 veröffentlichte der Interdisziplinäre Arbeitskreis für Mund- und Gesichtsschmerzen in der Deutschen Gesellschaft zum Studium des Schmerzes Empfehlungen zur Diagnostik und Klassifikation von Patienten mit Schmerzen im Bereich der Kaumuskulatur und/oder Kiefergelenke. Ziele der vorliegenden Publikation sind eine Bestandsaufnahme und Aktualisierung der damals gemachten Vorschläge. Ergebnisse: Sichtung und Bewertung der nach Veröffentlichung der Empfehlungen erschienenen Fachliteratur (bis Dezember 2005) zeigen, dass sich das zweiachsige Stufenkonzept zur Erfassung somatischer und psychosozialer Parameter orofazialer Schmerzen bewährt hat. Einzelne Aspekte der Empfehlungen wurden in Form wissenschaftlicher Belege weiter konkretisiert. Schlussfolgerungen: Die vorgeschlagenen Empfehlungen spiegeln die aktuellen Entwicklungen in der Schmerzmedizin wider. Insbesondere in der Zahnärzteschaft sollten sie daher eine noch breitere Verankerung finden als bishe
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Role of State Policy in Renewable Energy Development
State policies can support renewable energy development by driving markets, providing certainty in the investment market, and incorporating the external benefits of the technologies into cost/benefit calculations. Using statistical analyses and policy design best practices, this paper quantifies the impact of state-level policies on renewable energy development in order to better understand the role of policy on development and inform policy makers on the policy mechanisms that provide maximum benefit. The results include the identification of connections between state policies and renewable energy development, as well as a discussion placing state policy efforts in context with other factors that influence the development of renewable energy (e.g. federal policy, resource availability, technology cost, public acceptance)
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