By shifting the reference system for the local-density approximation (LDA) from the electron gas to other model systems one obtains a new class of density functionals, which by design account for the correlations present in the chosen reference system. This strategy is illustrated by constructing an explicit LDA for the one-dimensional Hubbard model. While the traditional ab initio LDA is based on a Fermi liquid (the electron gas), this one is based on a Luttinger liquid. First applications to inhomogeneous Hubbard models, including one containing a localized impurity, are reported. 71.15.Mb, 71.10.Pm, 71.10.Fd, 71.27.+a Density-functional theory (DFT)  is the basis of almost all of todays electronic-structure theory, and much of materials science and quantum chemistry. Many-body effects enter DFT via the exchange-correlation (xc) functional, which is commonly approximated by the localdensity approximation (LDA) . The essence of the LDA is to locally approximate the xc energy of the inhomogeneous system under study by that of the homogeneous electron gas. This electron gas plays the role of a reference system, whose correlations are transfered by the LDA into the DFT description of the inhomogeneous system. The most popular improvement upon the LDA are generalized gradient approximations , whose basic philosophy is to abandon the requirement of homogeneity of the reference system. This system, however, is normally still the interacting electron gas .In the present paper we propose to explore a different paradigm for the construction of novel density functionals: instead of sticking to the electron gas as a reference system, and abandoning homogeneity, it may sometimes be advantageous to do the reverse: stick to homogeneity (and thus to the LDA) but abandon the electron gas as a reference system. The new reference system is chosen such that it accounts for the correlations present in the inhomogeneous system under study.The only requirement for the reference system is that in the absence of any spatially varying external potential its xc energy must be known exactly or to a high degree of numerical precision. Besides the electron gas (or Jellium model) there are many other physically interesting model systems that satisfy this criterium. Most notably among these is a large class of low-dimensional models which can be solved exactly by Bethe Ansatz (BA) techniques or bosonisation (in one dimension, e.g., the repulsive and the attractive Hubbard model, the hard-core Fermi and Bose gases, the Heisenberg, the supersymmetric t-J, and the Tomonaga-Luttinger model [3,4]). The solutions to these models in the homogeneous case can be used instead of the electron gas to construct LDA functionals that can then be applied to study these models also in inhomogeneous situations. The main advantage offered by a DFT treatment of such models is the gain in simplicity that arises from mapping the inhomogeneous interacting many-body system onto a noninteracting auxiliary system, which is diagonalized much more easily...
Iron is the fourth most common element by mass in the Earth's crust and forms compounds in several oxidation states. Iron (hydr)oxides, some of which form inherently and exclusively in the nanometre-size range, are ubiquitous in nature and readily synthesized. These facts add up to render many Fe (hydr)oxides suitable as catalysts, and it is hardly surprising that numerous studies on the applications of Fe (hydr)oxides in catalysis have been published. Moreover, the abundant availability of a natural Fe source from rocks and soils at minimal cost makes the potential use of these as heterogeneous catalyst attractive.Besides those Fe (hydr)oxides that are inherently nanocrystalline (ferrihydrite, Fe5HO8.4H2O, and feroxyhyte, δ’-FeOOH), magnetite (Fe3O4) is often used as a catalyst because it has a permanent magnetization and contains Fe in both the divalent and trivalent states. Hematite, goethite and lepidocrocite have also been used as catalysts in their pure forms, doped with other cations, and as composites with carbon, alumina and zeolites among others.In this review we report on the use of synthetic and natural Fe (hydr)oxides as catalysts in environmental remediation procedures using an advanced oxidation process, more specifically the Fenton-like system, which is highly efficient in generating reactive species such as hydroxyl radicals, even at room temperature and under atmospheric pressure. The catalytic efficiency of Fe (hydr)oxides is strongly affected by factors such as the Fe oxidation state, surface area, isomorphic substitution of Fe by other cations, pH and temperature.
This study evaluated the feasibility of using the International Caries Detection and Assessment System (ICDAS-II) in epidemiological surveys and compared ICDAS with WHO criteria. Two hundred and fifty-two children (36–59 months old) in Amparo, Brazil, were each examined by 2 examiners using ICDAS-II or WHO criteria. Dmf-t, dmf-s, caries prevalence and examination time were calculated using both systems. ICDAS-II was comparable to standard criteria when the cut-off point was score 3. Examination by ICDAS-II took twice as long as by WHO criteria. In conclusion, ICDAS-II, besides providing information on non-cavitated caries lesions, can generate data comparable to previous surveys which used WHO criteria.
A modified numerical renormalization-group procedure, preserving the particle-hole asymmetry of the two-impurity Kondo model, calculates the susceptibility, over 13 decades of temperature, and lowtemperature specific heat. For large ferromagnetic RKKY couplings, a two-stage Kondo effect screens the triplet-correlated moments. For large antiferromagnetic couplings, the impurities develop singlet correlations and contribute Van Vleck terms to the low-temperature properties. For vanishing particlehole asymmetry, previously found critical behavior emerges at low temperatures. PACS numbers: 75.20.Hr, 75.30.Hx, 75.30.Mb, 75.40.Cx The two-impurity Kondo problem stands out in the theory of strongly correlated electrons. Its Hamiltonian has two energy scales: the conduction-electron mediated (RKKY ) interaction I, which tends to align the impurity spins, and the Kondo temperature T K , below which the conduction band tends to screen their magnetic moments [2,3]. These competing energies generate Fermiand non-Fermi-liquid behaviors [4-6], ferromagnetic and antiferromagnetic correlations, Curie and Van Vleck susceptibilities, one-and two-stage Kondo effects , and a strange sensitivity to particle-hole asymmetry . All this richness surfaces in our susceptibility and lowtemperature specific-heat curves. Our unified picture accommodates every breakthrough in the long history of the model.A scaling analysis of the susceptibility predicted, among other features, a two-stage Kondo effect and a smooth transition from the Kondo regime (k B T K ¿ jIj) to the RKKY regime (jIj ¿ k B T K ) . Years later, a numerical renormalization-group (NRG) diagonalization  of a somewhat different, particle-hole symmetric Hamiltonian discovered an unstable, non-Fermi-liquid fixed point separating the antiferromagnetic RKKY regime from the Kondo regime [5,9]. By the time the low-energy spectrum and its physical properties were calculated analytically [6,11], it had become apparent that only special models, which we call symmetrical, encompass this fixed point: The model Hamiltonian must remain invariant under a special particle-hole transformation . Moreover, since this symmetry generally generates only ferromagnetic RKKY interactions, to allow tuning to the critical antiferromagnetic coupling the model must have an additional, adjustable impurity-impurity interaction . Generally asymmetric  and lacking the added interaction, the conventional model displays only Fermi-liquid behavior .The critical properties understood, interest reverts to more general features. Our NRG diagonalization  of the (conventional) two-impurity Hamiltonian yields quantitatively reliable temperature-dependent uniform susceptibilities. The results fit the image of temperature-dependent screening in competition with impurity alignment [4,7], and, in particular, substantiate the conclusions of Jayaprakash, and Wilkins , from the antiferromagnetic formation of an impurity singlet to the ferromagnetic two-stage Kondo...
A total of 55 women underwent sphincteroplasty for the treatment of faecal incontinence related to anterior defects. Patients were followed prospectively for a mean of 29 months to evaluate the outcome overall and according to age. All patients were evaluated clinically by means of a questionnaire and graded using an incontinence scoring system ranging from 0 (perfect continence) to 20 (complete incontinence). Some 52 patients (95 per cent) had had a previous vaginal delivery and 30 (55 per cent) had a history of previous anal sphincter repair. Physiological and functional parameters in patients with a successful outcome (n = 39) were compared with those in patients with a poor outcome (n = 16). The results were also compared in patients under (n = 39) and over (n = 16) 60 years of age. Overall, patients with a successful outcome had a significant change in mean and maximal resting and squeeze pressures. These changes correlated well with the increase in the high-pressure zone (HPZ) length from 1.0-2.2 cm (P = 0.0002) and with functional outcome (change in incontinence score from 15.3 to 5.8; P < 0.0001). In patients over 60 years of age, a significant change in mean squeeze pressure (P = 0.03) and HPZ length (P = 0.01) was noted and correlated with functional outcome (change in incontinence score from 14.3 to 6.4; P < 0.0001). A successful outcome after anterior sphincteroplasty is related to improvement in sphincter function even in an older population. These results demonstrate that age itself does not seem to be a predictor of poor outcome. Patients should not be denied a repair exclusively on grounds of age.
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