TIME-DEPENDENT DENSITY FUNCTIONAL THEORY

Time-dependent density functional theory (TDDFT) can be viewed as an exact reformulation of time-dependent quantum mechanics, where the fundamental variable is no longer the many-body wave function but the density. This time-dependent density is determined by solving an auxiliary set of noninteracting Schrodinger equations, the Kohn-Sham equations. The nontrivial part of the many-body interaction is contained in the so-called exchange-correlation potential, for which reasonably good approximations exist. Within TDDFT two regimes can be distinguished: (a) If the external time-dependent potential is "small," the complete numerical solution of the time-dependent Kohn-Sham equations can be avoided by the use of linear response theory. This is the case, e.g., for the calculation of photoabsorption spectra. (b) For a "strong" external potential, a full solution of the time-dependent Kohn-Sham equations is in order. This situation is encountered, for instance, when matter interacts with intense laser fields. In this review we give an overview of TDDFT from its theoretical foundations to several applications both in the linear and in the nonlinear regime.

Time-dependent density functional theory: past, present, and future

Time-dependent density functional theory (TDDFT) is presently enjoying enormous popularity in quantum chemistry, as a useful tool for extracting electronic excited state energies. This article discusses how TDDFT is much broader in scope, and yields predictions for many more properties. We discuss some of the challenges involved in making accurate predictions for these properties.

Reproducibility in density functional theory calculations of solids

The widespread popularity of density functional theory has given rise to an extensive range of dedicated codes for predicting molecular and crystalline properties. However, each code implements the formalism in a different way, raising questions about the reproducibility of such predictions. We report the results of a community-wide effort that compared 15 solid-state codes, using 40 different potentials or basis set types, to assess the quality of the Perdew-Burke-Ernzerhof equations of state for 71 elemental crystals. We conclude that predictions from recent codes and pseudopotentials agree very well, with pairwise differences that are comparable to those between different high-precision experiments. Older methods, however, have less precise agreement. Our benchmark provides a framework for users and developers to document the precision of new applications and methodological improvements.

Prevalence and predictive factors for regional osteopenia in women with anorexia nervosa

BACKGROUND

Anorexia nervosa is highly prevalent among young women.

OBJECTIVE

To determine prevalence and predictive factors for regional bone loss.

DESIGN

Prospective cohort analysis.

SETTING

University hospital.

PATIENTS

130 women with anorexia nervosa.

MEASUREMENTS

Dual-energy x-ray absorptiometry.

RESULTS

The prevalence of osteopenia (-1.0 SD >/= T-score > -2.5 SD) and osteoporosis (T-score </= -2.5 SD) was 50% and 13% for the anterior-posterior spine, 57% and 24% for the lateral spine, and 47% and 16% for the total hip, respectively. Bone mineral density (BMD) was reduced by at least 1.0 SD at one or more skeletal sites in 92% of patients and by at least 2.5 SD in 38% of patients. Weight was the most consistent predictor of BMD at all skeletal sites. Twenty-three percent of patients were current estrogen users, and 58% were previous estrogen users. Bone mineral density did not differ by history of estrogen use at any site.

CONCLUSIONS

Bone mineral density is reduced at several skeletal sites in most women with anorexia nervosa. Weight, but not estrogen use, is a significant predictor of BMD in this population at all skeletal sites.

Exact factorization of the time-dependent electron-nuclear wave function

We present an exact decomposition of the complete wave function for a system of nuclei and electrons evolving in a time-dependent external potential. We derive formally exact equations for the nuclear and electronic wave functions that lead to rigorous definitions of a time-dependent potential energy surface (TDPES) and a time-dependent geometric phase. For the H(2)(+) molecular ion exposed to a laser field, the TDPES proves to be a useful interpretive tool to identify different mechanisms of dissociation.

Dual-wavelength ratiometric fluorescence measurement of the membrane dipole potential

The electrostatic potentials associated with cell membranes include the transmembrane potential (delta psi), the surface potential (psi s), and the dipole potential (psi D). psi D, which originates from oriented dipoles at the surface of the membrane, rises steeply just within the membrane to approximately 300 mV. Here we show that the potential-sensitive fluorescent dye 1-(3-sulfonatopropyl)-4-[beta[2-(di-n-octylamino)-6- naphthyl]vinyl]pyridinium betaine (di-8-ANEPPS) can be used to measure changes in the intramembrane dipole potential. Increasing the content of cholesterol and 6-ketocholestanol (KC), which are known to increase psi D in the bilayer, results in an increase in the ratio, R, of the dye fluorescence excited at 440 nm to that excited at 530 nm in a lipid vesicle suspension; increasing the content of phloretin, which lowers psi D, decreases R. Control experiments show that the ratio is insensitive to changes in the membrane's microviscosity. The lack of an isosbestic point in the fluorescence excitation and emission spectra of the dye at various concentrations of KC and phloretin argues against 1:1 chemical complexation between the dye and KC or phloretin. The macromolecular nonionic surfactant Pluronic F127 catalyzes the insertion of KC and phloretin into lipid vesicle and cell membranes, permitting convenient and controlled modulation of dipole potential. The sensitivity of R to psi D is 10-fold larger than to delta psi, whereas it is insensitive to changes in psi S. This can be understood in terms of the location of the dye chromophore with respect to the electric field profile associated with each of these potentials. These results suggest that the gradient in dipole potential occurs over a span s5 A, a short distance below the membrane-water interface. These approaches are easily adaptable to study the influence of dipole potentials on cell membrane physiology.

Prediction of severity of Gaucher's disease by identification of mutations at DNA level

The polymerase chain reaction was used to detect four mutations in the DNA of 47 unrelated patients with type I Gaucher's disease (94 Gaucher's disease alleles). Two of the mutations, 1226 and 1448, and a new mutation (XOVR) representing cross-over between the glucocerebrosidase gene and its closely linked pseudogene, were found. There were five genotypes--namely, 1226/1226, 1226/1448, 1226/XOVR, 1226/?, and ?/? (where "?" indicates that none of the four known mutations was present). Severity of the disease was assessed with a scoring index according to age at diagnosis and extent of organ involvement. Mutation 1226 was associated with a mild clinical phenotype, and mutation 1448 with a more severe phenotype. Mutation 1226 is the most common cause of Gaucher's disease in Jewish patients.

Single-channel parameters of gramicidin A,B, and C

The single-channel conductance lambda and the mean channel lifetime gamma of natural and synthetic gramicidins A, B, and C has been studied. Significant differences in delta were found between gramicidin A and B; both gramicidins differ only in one amino acid (tryptophan replaced by phenylaline). The distribution of lambda is narrow in glycerylmonooleate membranes but considerably broader in dioleoyl phosphatidylcholine and dioleoyl phosphatidylethanolamine membranes. The ratio of the single-channel conductances in glycerylmonooleate and dioleoyl phosphatidylcholine membranes is only about two and is considerable smaller than the conductance ratio of nonactin-mediated cation transport. This finding suggests that dipolar potentials at the membrane/solution interface have little influence on the conductance of the gramicidin channel.

Correlated electron-nuclear dynamics: exact factorization of the molecular wavefunction

It was recently shown [A. Abedi, N. T. Maitra, and E. K. U. Gross, Phys. Rev. Lett. 105, 123002 (2010)] that the complete wavefunction for a system of electrons and nuclei evolving in a time-dependent external potential can be exactly factorized into an electronic wavefunction and a nuclear wavefunction. The concepts of an exact time-dependent potential energy surface (TDPES) and exact time-dependent vector potential emerge naturally from the formalism. Here, we present a detailed description of the formalism, including a full derivation of the equations that the electronic and nuclear wavefunctions satisfy. We demonstrate the relationship of this exact factorization to the traditional Born-Oppenheimer expansion. A one-dimensional model of the H(2)(+) molecule in a laser field shows the usefulness of the exact TDPES in interpreting coupled electron-nuclear dynamics: we show how features of its structure indicate the mechanism of dissociation. We compare the exact TDPES with potential energy surfaces from the time-dependent Hartree-approach, and also compare traditional Ehrenfest dynamics with Ehrenfest dynamics on the exact TDPES.

Bronchial reactivity to inhaled histamine and annual rate of decline in FEV1 in male smokers and ex-smokers

We examined the relations between bronchial reactivity, baseline FEV1, and annual decline of height corrected FEV1 (delta FEV1/ht3) over 7.5 years in 227 men (117 smokers, 71 ex-smokers, and 39 non-smokers). Men with a clinical diagnosis of asthma or receiving bronchodilator treatment were excluded. Bronchial reactivity was determined as the provocation concentration (PC20) of inhaled histamine sufficient to reduce FEV1 by 20%; subjects were divided into reactors (PC20 less than or equal to 16 mg/ml) and non-reactors (PC20 greater than 16 mg/ml). Thirty per cent of smokers, 24% of ex-smokers, and 5% of non-smokers were reactors. When smokers who were reactors were compared with non-reactors, the reactors showed a lower baseline FEV1 as percentage predicted in 1981-2 (85% v 108%), and a faster delta FEV1/ht3 (14.1 v 9.2 ml/y/m3). Baseline FEV1 correlated with PC20 in both smokers (rs = 0.51) and ex-smokers (rs = 0.61), and all 15 subjects with an FEV1 under 80% of the predicted value were reactors. In ex-smokers delta FEV1/ht3 was similar in reactors and non-reactors (m 9.0 v 7.4 ml/y/m3), despite significant differences in baseline FEV1. When analysis was confined to men with a baseline FEV1 over 80% predicted, the prevalence of reactors was significantly increased among smokers and slightly increased among ex-smokers compared with non-smokers, though the mean FEV1 was higher in the non-smokers. Bronchial reactivity was not increased in smokers aged 35 years or less. In smokers delta FEV1/ht3 was faster in those with a personal history of allergy (usually allergic rhinitis), but was not related to a family history of allergic disease, total serum immunoglobulin E level, absolute blood eosinophil count, or skinprick test score. delta FEV1/ht3 was also faster in all subjects taking beta blocker drugs. Thus increased bronchial reactivity was associated with accelerated decline of FEV1 in smokers. Although the association could be a consequence of a lower lower baseline FEV1, a trend towards increased reactivity was found in smokers with normal baseline FEV1 and delta FEV1/ht3 was dissociated from increased reactivity in ex-smokers. These findings are compatible with the "Dutch hypothesis," but the association between allergic features and accelerated delta FEV1/ht3 was relatively weak, and increased reactivity may follow rather than precede the onset of smoking.

Performance of the ATLAS trigger system in 2015

During 2015 the ATLAS experiment recorded [Formula: see text] of proton-proton collision data at a centre-of-mass energy of [Formula: see text]. The ATLAS trigger system is a crucial component of the experiment, responsible for selecting events of interest at a recording rate of approximately 1 kHz from up to 40 MHz of collisions. This paper presents a short overview of the changes to the trigger and data acquisition systems during the first long shutdown of the LHC and shows the performance of the trigger system and its components based on the 2015 proton-proton collision data.

Evidence for a gonadotropin from nonpregnant subjects that has physical, immunological, and biological similarities to human chorionic gonadotropin

Substances from urinary extracts of normal, nonpregnant subjects and human pituitary gonadotropin preparations were found to react similarly to human chorionic gonadotropin (hCG) in a radioimmunoassay system that is highly specific for hCG and without crossreactivity to human luteinizing hormone (hLH). The antiserum was produced in a rabbit immunized with a bovine albumin conjugate of the unique carboxyl-terminal peptide (residues 123-145) isolated from a tryptic digest of the reduced, S-carboxymethylated hCGbeta subunit. The antibody recognition site on the peptide was found to reside on the last 15 amino acid residues of the carboxyl-terminal peptide, as evidenced by the competitive binding activities against 125I-labeled hCG of a series of peptides chemically synthesized according to the carboxyl-terminal sequence of HCGbeta. In order to elucidate the nature of the crossreacting substance in urinary extracts, a human postmenopausal urinary preparation (Pergonal) and a kaolin-acetone extract of urine from a patient with Klinefelter's syndrome were subjected to gel chromatography on Sephadex G-100. The results indicate that fractions showing immunocrossreactivity with the antiserum to hCGbeta-carboxyl-terminal peptide coeluted with 125I-labeled hCG which was separated distinctly from hLH. The same fractions from this postmenopausal urinary gonadotropin preparation exhibited in vitro biological activity proportional to the immunocrossreactivity of the hCG-specific antiserum. Concentration of postmenopausal women's urine by acetone precipitation retained approximately five times more immunoreactivity per unit volume than kaolin-acetone extraction, when assayed with the antiserum to hCGbeta-carboxyl-terminal peptide.

A comparison of BRCA1 mutation analysis by direct sequencing, SSCP and DHPLC

The most sensitive screening technique for genes that predispose patients for particular cancers is direct sequencing. However, sequencing of complex genes is technically demanding, costly and time-consuming. We have tested alternate screening techniques to find a fast sensitive method for detecting alterations of DNA in the large BRCA1 gene prior to sequencing. Sequencing of this gene is particularly arduous because it lacks clearly defined mutation sites. The single-strand conformation polymorphism (SSCP) technique is one of the most frequently used pre-screening methods but its sensitivity and efficiency is not completely satisfying. We have compared the SSCP assay with a newly developed technique called denaturing high performance liquid chromatography (DHPLC) to screen the BRCAl gene. We studied 23 patients at high risk for early onset breast and ovarian cancer and four controls. In these patients, a total of 113 fragments with sequence variations in the BRCA1 gene could be identified. The DHPLC technique resolved 100% of the DNA alterations that were observed in cycle sequencing. In contrast, mutation analysis by SSCP accounted for 94% of the detected variations. In addition, DHPLC screening allowed us to discriminate between different alterations in a single fragment, because of the characteristic elution profiles of the DNA molecules. Polymorphisms that were present in our samples could be predicted by means of DHPLC testing independently of sequence analysis. We conclude that DHPLC is a highly potent screening method for genetic analyses. It is highly sensitive, efficient and economical and can be automated.

Laparoscopic compared with conventional treatment of acute adhesive small bowel obstruction

BACKGROUND

Although laparoscopy may be associated with fewer intra-abdominal adhesions and quicker recovery of bowel function, it remains unclear whether patients with acute small bowel obstruction (SBO) might benefit from laparoscopic techniques.

METHOD

The results of patients with acute SBO treated laparoscopically (LAP; n = 52) and conventionally (CONV; n = 52) were compared in a retrospective matched-pair analysis. Conversions were included in the laparoscopic group.

RESULTS

Complete laparoscopic treatment was performed in 25 patients (48.1 per cent). Major intraoperative complications occurred in 15 patients in the LAP group and eight in the CONV group (P = 0.156). Intraoperative perforations were more frequent in patients who had undergone more than one previous laparotomy (P = 0.066). Postoperative complications occurred in ten patients (19.2 per cent) in the LAP group and in 21 patients (40.4 per cent) who had conventional surgery (P = 0.032). Bowel movements started 3.5 days after operation in the LAP group and 4.4 days after conventional operation (P = 0.001). The length of hospital stay was 11.3 and 18.1 days respectively (P < 0.001).

CONCLUSION

Laparoscopic treatment of acute SBO was feasible in about half of these patients. Postoperative recovery was improved after laparoscopic procedures but the risk of intraoperative complications increased. A laparoscopic approach seems justified in a subset of patients.