Ground state pressure and energy density of an interacting homogeneous Bose gas in two dimensions

We consider an interacting homogeneous Bose gas at zero temperature in two spatial dimensions. The properties of the system can be calculated as an expansion in powers of g, where g is the coupling constant. We calculate the ground state pressure and the ground state energy density to second order in the quantum loop expansion. The renormalization group is used to sum up leading and subleading logarithms from all orders in perturbation theory. In the dilute limit, the renormalization group improved pressure and energy density are expansions in powers of the T ^2B and T ^2Bln(T ^2B), respectively, where T ^2B is the two-body T-matrix. Received 19 April 2002 Published online 13 August 2002     

General excitations in time-dependent density functional theory

A general framework within time-dependent density functional theory is presented for the calculation of excitations to states of arbitrary multiplicity in molecular systems with a non-singlet ground state. The proposed approach combines generalized orbital excitation operators designed to generate excited states which have well-defined multiplicities and the noncollinear formulation of density functional theory and it can be straightforwardly implemented in currently existing density functional programs.     

Wasserverbrückte nickelorganoverbindung: Kristall- und molekülstruktur von bis(2,2′-bipyridin-2-methyl-pent-2-enal-nickel) · H2O [(bipy)Ni(C2H5ChC(CH3)CHO)]2 · H2O

The structure of the dimeric complex [(bipy)Ni(MEA)]₂ · H₂O (MEA = 2-methylpent-2-enal (α-methyl-β-ethylacrolein)) was determined by X-ray structural analysis (space group P$\text{1}$, a 10.843(4), b 9.650(3), c 17.116(2) Å, Z = 4, R = 0.05). The MEA ligand is not exclusively coordinated through the olefinic group, but there is however, interaction with the C atom of the neighbouring CO group (NiC distances 2.28 and 2.40 Å in both symmetrically independent molecules). The true bonding situation can be described as in between purely olefinic and purely π-allylic. Two molecules of (bipy)Ni(MEA) are connected by a molecule of water, which bonds asymmetrically to the two oxygen atoms of both aldehyde groups. The compound described is apparently the first example of an organonickel compound with bound water. The compound's importance for complex catalysed aldol condensations is discussed.     

Functional magnetic resonance imaging with intermolecular multiple-quantum coherences

For the first time, we demonstrate here functional magnetic resonance imaging (fMRI) using intermolecular multiple-quantum coherences (iMQCs). iMQCs are normally not observed in liquid-state NMR because dipolar interactions between spins average to zero. If the magnetic isotropy of the sample is broken through the use of magnetic field gradients, dipolar couplings can reappear, and hence iMQCs can be observed. Conventional (BOLD) fMRI measures susceptibility variations averaged over each voxel. In the experiment performed here, the sensitivity of iMQCs to frequency variations over mesoscopic and well-defined distances is exploited. We show that iMQC contrast is qualitatively and quantitatively different from BOLD contrast in a visual stimulation task. While the number of activated pixels is smaller in iMQC contrast, the intensity change in some pixels exceeds that of BOLD contrast severalfold.     

Determination and confirmation of malachite green and leucomalachite green residues in salmon using liquid chromatography/mass spectrometry with no-discharge atmospheric pressure chemical ionization

A liquid chromatography/mass spectrometry (LC/MS) method was developed to quantitate and confirm residues of leucomalachite green (LMG) in salmon tissue after their conversion to chromic malachite green (MG) in the extraction process. The method uses no-discharge atmospheric pressure chemical ionization (APCI) in conjunction with an ion-trap instrument to generate product-ion spectra. In the sample preparation procedure, salmon tissue is extracted with acetonitrile/buffer, the LMG residue is partitioned into methylene chloride, the LMG is converted to MG using an organic oxidizing agent, and the MG is isolated on alumina/propylsulfonic acid solid-phase extraction cartridges. The method was validated by fortifying salmon with different levels of LMG, and then detecting the residue as MG The LC/MS conditions, including a comparison of electrospray and no-discharge APCI, were evaluated and optimized. MG was not confirmed in any of the control tissue extracts, and all fortified samples analyzed during validation met the confirmation criteria as described. In addition to providing confirmatory data, this method can provide an alternative method for quantitation of MG in salmon. The recoveries of LMG measured as MG by this LC/MS method, at fortification levels of 1-10 ng/g were very high (86-109%), with low relative standard deviation(RSD) values (6.4-13%). The results agreed very closely with those obtained for the same extracts using an LCNIS procedure, indicating that matrix suppression was not an issue. The presence of LMG in salmon tissue samples fortified at 0.25 ng/g was confirmed by this method, with an average recovery of 70.1% and an RSD of 12.0%. Sample extracts from fish exposed to MG were also analyzed.     

Determination of Formation Regions of Titanium Phosphates; Determination of the Crystal Structure ofβ-Titanium Phosphate, Ti(PO4)(H2PO4), from Neutron Powder Data

The formation region of the various types of layered titanium hydrogen phosphate hydrates was investigated. The materials were prepared by hydrothermal methods, treating amorphous titanium phosphate with phosphoric acid (8 to 16M) in the temperature range 175 to 250°C. The materials obtained were:α-Ti(HPO₄)₂·H₂O,γ-Ti(PO₄)(H₂PO₄)·2H₂O, and its anhydrous formβ-Ti(PO₄)(H₂PO₄). The structure ofβ-Ti(PO₄)(H₂PO₄) has been determined by Rietveld powder refinement of high resolution neutron diffraction data. The structure is refined in the monoclinic space groupP2₁/n(No. 14). The unit cell parameters are:a=18.9503(4) Å,b=6.3127(1) Å,c=5.1391(1) Å,β=105.366(2)°;Z=4. The final agreement factors were:R_p=2.9% andR_wp=3.8%. The structure ofβ-Ti(PO₄)(H₂PO₄) is built from TiO₆octahedra linked together by tertiary phosphate (PO₄) and dihydrogen phosphate ((OH)₂PO₂) tetrahedra. The layers are held together by hydrogen bonds.     

Stem cell survival is severely compromised by the thymidineanalog EdU (5-ethynyl-2′-deoxyuridine), an alternative to BrdU for proliferation assays and stem cell tracing

Stem cell therapy has opened up the possibility of treating numerous degenerating diseases. However, we are still merely at the stage of identifying appropriate sources of stem cells and exploring their full differentiation potential. Thus, tracking the stem cells upon in vivo engraftment and during in vitro co-culture is very important and is an area of research embracing many pitfalls. 5-Ethynyl-2′-deoxyuridine (EdU), a rather new thymidine analog incorporated into DNA, has recently been suggested to be a novel highly valid alternative to other dyes for labeling of stem cells and subsequent tracing of their proliferation and differentiation ability. However, our results herein do not at any stage support this recommendation, since EdU severely reduces the viability of stem cells. Accordingly, we found that transplanted EdU-labeled stem cells hardly survive upon in vivo transplantation into regenerating muscle, whereas stem cells labeled in parallel with another dye survived very well and also participated in myofiber formation. Similar data were obtained upon in vitro myogenic culture, and further analysis showed that EdU reduced cell numbers by up to 88 % and increased the cell volume of remaining cells by as much as 91 %. Even at low EdU concentrations, cell survival and phenotype were substantially compromised, and the myogenic differentiation potential was inhibited. Since we examined both primary derived cells and cell lines from several species with the same result, this appears to be a common trait of EdU. We therefore suggest that EdU labeling should be avoided (or used with precaution) for stem cell tracing purposes.

Direct optical detection of singlet oxygen from a single cell

Singlet oxygen has been detected in single nerve cells by its weak 1270 nm phosphorescence (a1deltag --> X3sigmag-) upon irradiation of a photosensitizer incorporated in the cell. Thus, one can now consider the application of direct optical imaging techniques to mechanistic studies of singlet oxygen at the single-cell level.