Two-Particle-Self-Consistent Approach for the Hubbard Model

Even at weak to intermediate coupling, the Hubbard model poses a formidable challenge. In two dimensions in particular, standard methods such as the Random Phase Approximation are no longer valid since they predict a finite temperature antiferromagnetic phase transition prohibited by the Mermin-Wagner theorem. The Two-Particle-Self-Consistent (TPSC) approach satisfies that theorem as well as particle conservation, the Pauli principle, the local moment and local charge sum rules. The self-energy formula does not assume a Migdal theorem. There is consistency between one- and two-particle quantities. Internal accuracy checks allow one to test the limits of validity of TPSC. Here I present a pedagogical review of TPSC along with a short summary of existing results and two case studies: a) the opening of a pseudogap in two dimensions when the correlation length is larger than the thermal de Broglie wavelength, and b) the conditions for the appearance of d-wave superconductivity in the two-dimensional Hubbard model.Comment: Chapter in "Theoretical methods for Strongly Correlated Systems", Edited by A. Avella and F. Mancini, Springer Verlag, (2011) 55 pages. Misprint in Eq.(23) corrected (thanks D. Bergeron

Spatiotemporal Properties of the Action Potential Propagation in the Mouse Visual Cortical Slice Analyzed by Calcium Imaging

The calcium ion (Ca2+) is an important messenger for signal transduction, and the intracellular Ca2+ concentration ([Ca2+]i) changes in response to an excitation of the cell. To reveal the spatiotemporal properties of the propagation of an excitatory signal with action potentials in the primary visual cortical circuit, we conducted a Ca2+ imaging study on slices of the mouse visual cortex. Electrical stimulation of layer 4 evoked [Ca2+]i transients around the stimulus electrode. Subsequently, the high [Ca2+]i region mainly propagated perpendicular to the cortical layer (vertical propagation), with horizontal propagation being restricted. When the excitatory synaptic transmission was blocked, only weak and concentric [Ca2+]i transients were observed. When the action potential was blocked, the [Ca2+]i transients disappeared almost completely. These results suggested that the action potential contributed to the induction of the [Ca2+]i transients, and that excitatory synaptic connections were involved in the propagation of the high [Ca2+]i region in the primary visual cortical circuit. To elucidate the involvement of inhibitory synaptic connections in signal propagation in the primary visual cortex, the GABAA receptor inhibitor bicuculline was applied. In this case, the evoked signal propagated from layer 4 to the entire field of view, and the prolonged [Ca2+]i transients were observed compared with the control condition. Our results suggest that excitatory neurons are widely connected to each other over the entire primary visual cortex with recurrent synapses, and inhibitory neurons play a fundamental role in the organization of functional sub-networks by restricting the propagation of excitation signals

Loop Diuretics Have Anxiolytic Effects in Rat Models of Conditioned Anxiety

A number of antiepileptic medications that modulate GABAA mediated synaptic transmission are anxiolytic. The loop diuretics furosemide (Lasix) and bumetanide (Bumex) are thought to have antiepileptic properties. These drugs also modulate GABAA mediated signalling through their antagonism of cation-chloride cotransporters. Given that loop diuretics may act as antiepileptic drugs that modulate GABAergic signalling, we sought to investigate whether they also mediate anxiolytic effects. Here we report the first investigation of the anxiolytic effects of these drugs in rat models of anxiety. Furosemide and bumetanide were tested in adult rats for their anxiolytic effects using four standard anxiety models: 1) contextual fear conditioning; 2) fear-potentiated startle; 3) elevated plus maze, and 4) open-field test. Furosemide and bumetanide significantly reduced conditioned anxiety in the contextual fear-conditioning and fear-potentiated startle models. At the tested doses, neither compound had significant anxiolytic effects on unconditioned anxiety in the elevated plus maze and open-field test models. These observations suggest that loop diuretics elicit significant anxiolytic effects in rat models of conditioned anxiety. Since loop diuretics are antagonists of the NKCC1 and KCC2 cotransporters, these results implicate the cation-chloride cotransport system as possible molecular mechanism involved in anxiety, and as novel pharmacological target for the development of anxiolytics. In view of these findings, and since furosemide and bumetanide are safe and well tolerated drugs, the clinical potential of loop diuretics for treating some types of anxiety disorders deserves further investigation

Presynaptic NMDA Receptors Mediate IPSC Potentiation at GABAergic Synapses in Developing Rat Neocortex

NMDA receptors are traditionally viewed as being located postsynaptically, at both synaptic and extrasynaptic locations. However, both anatomical and physiological studies have indicated the presence of NMDA receptors located presynaptically. Physiological studies of presynaptic NMDA receptors on neocortical GABAergic terminals and their possible role in synaptic plasticity are lacking.We report here that presynaptic NMDA receptors are present on GABAergic terminals in developing (postnatal day (PND) 12-15) but not older (PND21-25) rat frontal cortex. Using MK-801 in the recording pipette to block postsynaptic NMDA receptors, evoked and miniature IPSCs were recorded in layer II/III pyramidal cells in the presence of AMPA/KA receptor antagonists. Bath application of NMDA or NMDA receptor antagonists produced increases and decreases in mIPSC frequency, respectively. Physiologically patterned stimulation (10 bursts of 10 stimuli at 25 Hz delivered at 1.25 Hz) induced potentiation at inhibitory synapses in PND12-15 animals. This consisted of an initial rapid, large increase in IPSC amplitude followed by a significant but smaller persistent increase. Similar changes were not observed in PND21-25 animals. When 20 mM BAPTA was included in the recording pipette, potentiation was still observed in the PND12-15 group indicating that postsynaptic increases in calcium were not required. Potentiation was not observed when patterned stimulation was given in the presence of D-APV or the NR2B subunit antagonist Ro25-6981.The present results indicate that presynaptic NMDA receptors modulate GABA release onto neocortical pyramidal cells. Presynaptic NR2B subunit containing NMDA receptors are also involved in potentiation at developing GABAergic synapses in rat frontal cortex. Modulation of inhibitory GABAergic synapses by presynaptic NMDA receptors may be important for proper functioning of local cortical networks during development

Exploratory study on the quality control and assessment methods used for groundwater quality data in the National Groundwater Quality Monitoring Network (LMG), the Water Framework Directive Groundwater Quality Monitoring Programme (KMG) and the Provincial Groundwater Quality Monitoring Programme (PMG)

In Nederland bestaan drie monitoringsprogramma's die data verzamelen over de kwaliteit van het grondwater: een van het RIVM (het Landelijk Meetnet Grondwaterkwaliteit, LMG) en twee van de provincies (het KRW Monitoringsprogramma Grondwaterkwaliteit, KMG, en het Provinciale Monitoringsprogramma grondwaterkwaliteit, PMG). Er wordt aan gewerkt om deze data in één systeem onder te brengen, de Basisregistratie Ondergrond (BRO). Het is dan ook belangrijk dat de data onderling vergelijkbaar zijn. In dat verband heeft het RIVM in kaart gebracht hoe de data worden gevalideerd. Het bestaande protocol, dat de partijen voor de validatie gebruiken, geeft ruimte voor vrijheden op dit gebied. Uit de verkenning blijkt dat voor het protocol uiteenlopende software wordt gebruikt om de data te controleren en te beoordelen. Bovendien worden de controle en beoordeling door verschillende partijen uitgevoerd (het RIVM, de provincies of een ingehuurde partij). Ook verschilt de manier waarop de data uiteindelijk worden vastgelegd. Deze constatering heeft geleid tot de afspraak in het Platform Meetnetbeheerders Bodem- en Grondwaterkwaliteit om te komen tot een geautomatiseerde standaard voor de controle en beoordeling van de data. Het is van belang dat dit gebeurt onder de verantwoordelijkheid van de partijen die de data aanleveren, de zogeheten bronhouders. Ondanks deze verschillen kan naar verwachting minstens 90 procent van de data gevalideerd en met voldoende kwaliteitsborging in de BRO worden opgenomen. 5 tot 10 procent behoeft een aanpassing die met feiten kan worden onderbouwd. Ongeveer 2 procent van de data staat dan nog ter discussie. Over dit laatste deel moet een panel van experts afwegen welke informatie in de BRO wordt opgenomen en op welke wijze. Ook voor de behandeling van deze groep data is het belangrijk om tot een uniforme werkwijze te komen.Three monitoring programmes are used in the Netherlands to collect data on the quality of the groundwater. RIVM operates the National Groundwater Quality Monitoring Network (LMG), while the WFD Groundwater Quality Monitoring Programme (KMG) and the Provincial Groundwater Quality Monitoring Programme (PMG) are operated by the provinces. The groundwater quality data of these programmes are currently being integrated into a single system, the Key Register of the Subsurface (Basisregistratie ondergrond, BRO). It is important that the data are comparable. RIVM has therefore analysed how these data are validated. The validation protocol used by the different organisations, allows some freedom in this respect. . The exploratory study shows that various types of software are used to control and assess the data. Furthermore, the quality control and assessment are carried out by different parties (RIVM, the provinces or a hired party). The way in which the data are ultimately documented also varies. These observations have led to an agreement to develop an automated standard for data control and assessment. It is important that this takes place under the responsibility of the parties delivering the data, that is, the so called source owners. Despite the above differences, it is expected that at least 90% of the data in the three monitoring programmes can be included in the BRO with sufficient quality assurance. Between 5 - 10% of the data need adjustment that can be underpinned by facts. Around 2% of the data will still need some discussion. A panel of experts will have to decide which of these data should be included in the BRO and, if so, how this should be done. It is also crucial that a uniform method is developed for handling of this data.Geonovu

Verkenning werkwijze controle en beoordeling grondwaterkwaliteitsdata in LMG, KMG, PMG

In Nederland bestaan drie monitoringsprogramma's die data verzamelen over de kwaliteit van het grondwater: een van het RIVM (het Landelijk Meetnet Grondwaterkwaliteit, LMG) en twee van de provincies (het KRW Monitoringsprogramma Grondwaterkwaliteit, KMG, en het Provinciale Monitoringsprogramma grondwaterkwaliteit, PMG). Er wordt aan gewerkt om deze data in één systeem onder te brengen, de Basisregistratie Ondergrond (BRO). Het is dan ook belangrijk dat de data onderling vergelijkbaar zijn. In dat verband heeft het RIVM in kaart gebracht hoe de data worden gevalideerd. Het bestaande protocol, dat de partijen voor de validatie gebruiken, geeft ruimte voor vrijheden op dit gebied. Uit de verkenning blijkt dat voor het protocol uiteenlopende software wordt gebruikt om de data te controleren en te beoordelen. Bovendien worden de controle en beoordeling door verschillende partijen uitgevoerd (het RIVM, de provincies of een ingehuurde partij). Ook verschilt de manier waarop de data uiteindelijk worden vastgelegd. Deze constatering heeft geleid tot de afspraak in het Platform Meetnetbeheerders Bodem- en Grondwaterkwaliteit om te komen tot een geautomatiseerde standaard voor de controle en beoordeling van de data. Het is van belang dat dit gebeurt onder de verantwoordelijkheid van de partijen die de data aanleveren, de zogeheten bronhouders. Ondanks deze verschillen kan naar verwachting minstens 90 procent van de data gevalideerd en met voldoende kwaliteitsborging in de BRO worden opgenomen. 5 tot 10 procent behoeft een aanpassing die met feiten kan worden onderbouwd. Ongeveer 2 procent van de data staat dan nog ter discussie. Over dit laatste deel moet een panel van experts afwegen welke informatie in de BRO wordt opgenomen en op welke wijze. Ook voor de behandeling van deze groep data is het belangrijk om tot een uniforme werkwijze te komen