66 research outputs found
Spin-Charge Separation and Kinetic Energy in the t-J Model
I show that spin-charge separation in 2-D t-J model leads to an increase of
kinetic energy. Using a sum rule, I derive an exact expression for the lowest
possible KE (E_{bound}) for any state without doubly occupied sites. KE of
relevant slave-boson and Schwinger-boson mean-field states -- which exhibit
complete spin-charge separation -- are found to be much larger than E_{bound}.
Examination of n(k) shows that the large increse in KE is due to excessive
depletion of electrons from the bottom of the band (Schwinger boson) and of
holes from the top (slave boson). To see whether the excess KE is simply due to
poor treatment of the constraints, I solve the constraint problem analytically
for the Schwinger boson case in the J = 0 limit. This restores gauge
invariance, incorrectly violated in MF theories. The result is a generalized
Hartree-Fock state of the Hubbard model, but one that includes spin waves. Even
after constraints are imposed correctly, the KE remains much larger than
E_{bound}. These results support the notion, advanced earlier [PRB 61, 8663
(2000)] that spin-charge separation in the MF state costs excessive KE, and
makes the state unstable toward recombination processes which lead to
superconductivity in d = 2 and a Fermi liquid state in higher dimensions.Comment: 13 pages, LateX plus three figures. To appear in Phys Rev B Typos
correcte
B NMR study of pure and lightly carbon doped MgB superconductors
We report a B NMR line shape and spin-lattice relaxation rate
() study of pure and lightly carbon doped MgBC for
, 0.02, and 0.04, in the vortex state and in magnetic field of 23.5 kOe.
We show that while pure MgB exhibits the magnetic field distribution from
superposition of the normal and the Abrikosov state, slight replacement of
boron with carbon unveils the magnetic field distribution of the pure Abrikosov
state. This indicates a considerable increase of with carbon doping
with respect to pure MgB. The spin-lattice relaxation rate
demonstrates clearly the presence of a coherence peak right below in pure
MgB, followed by a typical BCS decrease on cooling. However, at
temperatures lower than K strong deviation from the BCS behavior is
observed, probably from residual contribution of the vortex dynamics. In the
carbon doped systems both the coherence peak and the BCS temperature dependence
of weaken, an effect attributed to the gradual shrinking of the
hole cylinders of the Fermi surface with electron doping.Comment: 8 pages, 6 figures, submitted to Phys. Rev.
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Response to “Comment on ‘Adoption of Point-of-Use Chlorination for Household Drinking Water Treatment: A Systematic Review’”
Adoption of Point-of-Use Chlorination for Household Drinking Water Treatment: A Systematic Review
BackgroundCentralized chlorination of urban piped water supplies has historically contributed to major reductions in waterborne illness. In locations without effective centralized water treatment, point-of-use (POU) chlorination for households is widely promoted to improve drinking water quality and health. Realizing these health benefits requires correct, consistent, and sustained product use, but real-world evaluations have often observed low levels of use. To our knowledge, no prior reviews exist on adoption of chlorine POU products.ObjectivesOur objectives were to identify which indicators of adoption are most often used in chlorine POU studies, summarize levels of adoption observed, understand how adoption changes over time, and determine how adoption is affected by frequency of contact between participants and study staff.MethodsWe conducted a systematic review of household POU chlorination interventions or programs from 1990 through 2021 that reported a quantitative measure of adoption, were conducted in low- and middle-income countries, included data collection at households, and reported the intervention start date.ResultsWe identified 36 studies of household drinking water chlorination products that met prespecified eligibility criteria and extracted data from 46 chlorine intervention groups with a variety of chlorine POU products and locations. There was no consensus definition of adoption of household water treatment; the most common indicator was the proportion of household stored water samples with free chlorine residual >0.1 or 0.2mg/L. Among studies that reported either free or total chlorine-confirmed adoption of chlorine POU products, use was highly variable (across all chlorine intervention groups at the last time point measured in each study; range: 1.5%-100%; sample size-weighted median=47%; unweighted median=58%). The median follow-up duration among intervention groups was 3 months. On average, adoption declined over time and was positively associated with frequency of contact between respondents and study staff.DiscussionAlthough prior research has shown that POU chlorine products improve health when correctly and consistently used, a reliance on individual adoption for effective treatment is unlikely to lead to the widespread public health benefits historically associated with pressurized, centralized treatment of piped water supplies. https://doi.org/10.1289/EHP10839
Understanding the use of policy instruments for greenhouse gas management in Europe
A report from UCD Dublin as part of the International Collaboration Projects on Sustainable Societies for the Economic and Social Research Institute, Cabinet Office, Government of Japan, January 20, 2006
Understanding the use of policy instruments for greenhouse gas management in Europe
A report from UCD Dublin as part of the International Collaboration Projects on Sustainable Societies for the Economic and Social Research Institute, Cabinet Office, Government of Japan, January 20, 2006
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