A First Principles Theory of Nuclear Magnetic Resonance J-Coupling in solid-state systems

A method to calculate NMR J-coupling constants from first principles in extended systems is presented. It is based on density functional theory and is formulated within a planewave-pseudopotential framework. The all-electron properties are recovered using the projector augmented wave approach. The method is validated by comparison with existing quantum chemical calculations of solution-state systems and with experimental data. The approach has been applied to verify measured J-coupling in a silicophosphate structure, Si5O(PO4)6Comment: 9 page

Calculating NMR parameters in aluminophosphates : evaluation of dispersion correction schemes

Periodic density functional theory (DFT) calculations have recently emerged as a popular tool for assigning solid-state nuclear magnetic resonance (NMR) spectra. However, in order for the calculations to yield accurate results, accurate structural models are also required. In many cases the structural model (often derived from crystallographic diffraction) must be optimised (i.e., to an energy minimum) using DFT prior to the calculation of NMR parameters. However, DFT does not reproduce weak long-range "dispersion'' interactions well, and optimisation using some functionals can expand the crystallographic unit cell, particularly when dispersion interactions are important in defining the structure. Recently, dispersion-corrected DFT (DFT-D) has been extended to periodic calculations, to compensate for these missing interactions. Here, we investigate whether dispersion corrections are important for aluminophosphate zeolites (AlPOs) by comparing the structures optimised by DFT and DFT-D (using the PBE functional). For as-made AlPOs (containing cationic structure-directing agents (SDAs) and framework-bound anions) dispersion interactions appear to be important, with significant changes between the DFT and DFT-D unit cells. However, for calcined AlPOs, where the SDA-anion pairs are removed, dispersion interactions appear much less important, and the DFT and DFT-D unit cells are similar. We show that, while the different optimisation strategies yield similar calculated NMR parameters (providing that the atomic positions are optimised), the DFT-D optimisations provide structures in better agreement with the experimental diffraction measurements. Therefore, it appears that DFT-D calculations can, and should, be used for the optimisation of calcined and as-made AlPOs, in order to provide the closest agreement with all experimental measurements.PostprintPeer reviewe

Nonlocal pseudopotentials and magnetic fields

We show how to describe the coupling of electrons to non-uniform magnetic fields in the framework of the widely used norm-conserving pseudopotential appro ximation for electronic structure calculations. Our derivation applies to magnetic fields that are smooth on the scale of the core region. The method is validated by application to the calculation of the magnetic susceptibility of molecules. Our results are compared with high quality all electron quantum chemical results, and another recently proposed formalism.Comment: 4 pages, submitted to Physical Review Letter

Alien Registration- Pickard, Emma M. (Mars Hill, Aroostook County)

https://digitalmaine.com/alien_docs/34071/thumbnail.jp

Low attentional engagement makes attention network activity susceptible to emotional interference

The aim of this study was to investigate whether emotion-attention interaction depends on attentional engagement. To investigate emotional modulation of attention network activation, we used a functional MRI paradigm consisting of a visuospatial attention task with either frequent (high-engagement) or infrequent (low-engagement) targets and intermittent emotional or neutral distractors. The attention task recruited a bilateral frontoparietal network with no emotional interference on network activation when the attentional engagement was high. In contrast, when the attentional engagement was low, the unpleasant stimuli interfered with the activation of the frontoparietal attention network, especially in the right hemisphere. This study provides novel evidence for low attentional engagement making attention control network activation susceptible to emotional interference. © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins.Fil: Exposito, Veronica. Fundación para la Lucha contra las Enfermedades Neurológicas de la Infancia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Tampere; FinlandiaFil: Pickard, Natasha. California State University; Estados UnidosFil: Solbakk, Anne-Kristin. University of Oslo; NoruegaFil: Ogawa, Keith H.. Saint Mary's College Of California; Estados UnidosFil: Knight, Robert T.. California State University; Estados UnidosFil: Hartikainen, Kaisa M.. Universidad de Tampere; Finlandi

Robust Uptake of Magnetic Nanoparticles (MNPs) by Central Nervous System (CNS) Microglia: Implications for Particle Uptake in Mixed Neural Cell Populations

Magnetic nanoparticles (MNPs) are important contrast agents used to monitor a range of neuropathological processes; microglial cells significantly contribute to MNP uptake in sites of pathology. Microglial activation occurs following most CNS pathologies but it is not known if such activation alters MNP uptake, intracellular processing and toxicity. We assessed these parameters in microglial cultures with and without experimental ‘activation’. Microglia showed rapid and extensive MNP uptake under basal conditions with no changes found following activation; significant microglial toxicity was observed at higher particle concentrations. Based on our findings, we suggest that avid MNP uptake by endogenous CNS microglia could significantly limit uptake by other cellular subtypes in mixed neural cell populations

Urinary diversion and bladder reconstruction/replacement using intestinal segments for intractable incontinence or following cystectomy

Background Surgery performed to improve or replace the function of the diseased urinary bladder has been carried out for over a century. Main reasons for improving or replacing the function of the urinary bladder are bladder cancer, neurogenic bladder dysfunction, detrusor overactivity and chronic inflammatory diseases of the bladder (such as interstitial cystitis, tuberculosis and schistosomiasis). There is still much uncertainty about the best surgical approach. Options available at the present time include: (1) conduit diversion (the creation of various intestinal conduits to the skin) or continent diversion (which includes either a rectal reservoir or continent cutaneous diversion), (2) bladder reconstruction and (3) replacement of the bladder with various intestinal segments. Objectives To determine the best way of improving or replacing the function of the lower urinary tract using intestinal segments when the bladder has to be removed or when it has been rendered useless or dangerous by disease. Search methods We searched the Cochrane Incontinence Group Specialised Trials Register (searched 28 October 2011), which contains trials identified from the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE and CINAHL, and handsearching of journals and conference proceedings, and the reference lists of relevant articles. Selection criteria All randomised or quasi-randomised controlled trials of surgery involving transposition of an intestinal segment into the urinary tract. Data collection and analysis Trials were evaluated for appropriateness for inclusion and for risk of bias by the review authors. Three review authors were involved in the data extraction. Data were combined in a meta-analysis when appropriate. Main results Five trials met the inclusion criteria with a total of 355 participants. These trials addressed only five of the 14 comparisons pre-specified in the protocol. One trial reported no statistically significant differences in the incidence of upper urinary tract infection, uretero-intestinal stenosis and renal deterioration in the comparison of continent diversion with conduit diversion. The confidence intervals were all wide, however, and did not rule out important clinical differences. In a second trial, there was no reported difference in the incidence of upper urinary tract infection and uretero-intestinal stenosis when conduit diversions were fashioned from either ileum or colon. A meta-analysis of two trials showed no statistically significant difference in daytime or nocturnal incontinence amongst participants who were randomised to ileocolonic/ileocaecal segment bladder replacement compared to an ileal bladder replacement. However, one small trial suggested that bladder replacement using an ileal segment compared to using an ileocolonic segment may be better in terms of lower rates of nocturnal incontinence. There were no differences in the incidence of dilatation of upper tract, daytime urinary incontinence or wound infection using different intestinal segments for bladder replacement. However the data were reported for 'renal units', but not in a form that allowed appropriate patient-based paired analyses. No statistically significant difference was found in the incidence of renal scarring between anti-refluxing versus freely refluxing uretero-intestinal anastomotic techniques in conduit diversions and bladder replacement groups. Again, the outcome data were not reported as paired analysis or in form to carry out paired analysis. Authors' conclusions The evidence from the included trials was very limited. Only five studies met the inclusion criteria; these were small, of moderate or poor methodological quality, and reported few of the pre-selected outcome measures. This review did not find any evidence that bladder replacement (orthotopic or continent diversion) was better than conduit diversion following cystectomy for cancer. There was no evidence to suggest that bladder reconstruction was better than conduit diversion for benign disease. The clinical significance of data from one small trial suggesting that bladder replacement using an ileal segment compared to using an ileocolonic segment is better in terms of lower rates of nocturnal incontinence is uncertain. The small amount of usable evidence for this review suggests that collaborative multi centre studies should be organised, using random allocation where possible. This review is published as a Cochrane Review in the Cochrane Database of Systematic Reviews 2012, Issue 2. Cochrane Reviews are regularly updated as new evidence emerges and in response to comments and criticisms, and the Cochrane Database of Systematic Reviews should be consulted for the most recent version of the Review.</p

Quantum Monte Carlo study of a positron in an electron gas

Quantum Monte Carlo calculations of the relaxation energy, pair-correlation function, and annihilating-pair momentum density are presented for a positron immersed in a homogeneous electron gas. We find smaller relaxation energies and contact pair-correlation functions in the important low-density regime than predicted by earlier studies. Our annihilating-pair momentum densities have almost zero weight above the Fermi momentum due to the cancellation of electron-electron and electron-positron correlation effects