Strain-engineering Mott-insulating La2CuO4.

The transition temperature Tc of unconventional superconductivity is often tunable. For a monolayer of FeSe, for example, the sweet spot is uniquely bound to titanium-oxide substrates. By contrast for La2-xSrxCuO4 thin films, such substrates are sub-optimal and the highest Tc is instead obtained using LaSrAlO4. An outstanding challenge is thus to understand the optimal conditions for superconductivity in thin films: which microscopic parameters drive the change in Tc and how can we tune them? Here we demonstrate, by a combination of x-ray absorption and resonant inelastic x-ray scattering spectroscopy, how the Coulomb and magnetic-exchange interaction of La2CuO4 thin films can be enhanced by compressive strain. Our experiments and theoretical calculations establish that the substrate producing the largest Tc under doping also generates the largest nearest neighbour hopping integral, Coulomb and magnetic-exchange interaction. We hence suggest optimising the parent Mott state as a strategy for enhancing the superconducting transition temperature in cuprates.

Unified Picture for the Colossal Thermopower Compound FeSb2.

We identify the driving mechanism of the gigantic Seebeck coefficient in FeSb2 as the phonon-drag effect associated with an in-gap density of states that we demonstrate to derive from excess iron. We accurately model electronic and thermoelectric transport coefficients and explain the so far ill-understood correlation of maxima and inflection points in different response functions. Our scenario has far-reaching consequences for attempts to harvest the spectacular power factor of FeSb2.

Protected Fe valence in quasi-two-dimensional α-FeSi2.

We report the first comprehensive study of the high temperature form (α-phase) of iron disilicide. Measurements of the magnetic susceptibility, magnetization, heat capacity and resistivity were performed on well characterized single crystals. With a nominal iron d(6) configuration and a quasi-two-dimensional crystal structure that strongly resembles that of LiFeAs, α-FeSi2 is a potential candidate for unconventional superconductivity. Akin to LiFeAs, α-FeSi2 does not develop any magnetic order and we confirm its metallic state down to the lowest temperatures (T = 1.8 K). However, our experiments reveal that paramagnetism and electronic correlation effects in α-FeSi2 are considerably weaker than in the pnictides. Band theory calculations yield small Sommerfeld coefficients of the electronic specific heat γ = Ce/T that are in excellent agreement with experiment. Additionally, realistic many-body calculations further corroborate that quasi-particle mass enhancements are only modest in α-FeSi2. Remarkably, we find that the natural tendency to vacancy formation in the iron sublattice has little influence on the iron valence and the density of states at the Fermi level. Moreover, Mn doping does not significantly change the electronic state of the Fe ion. This suggests that the iron valence is protected against hole doping and indeed the substitution of Co for Fe causes a rigid-band like response of the electronic properties. As a key difference from the pnictides, we identify the smaller inter-iron layer spacing, which causes the active orbitals near the Fermi level to be of a different symmetry in α-FeSi2. This change in orbital character might be responsible for the lack of superconductivity in this system, providing constraints on pairing theories in the iron based pnictides and chalcogenides.

Downfolded self-energy of many-electron systems.

Starting from the full many-body Hamiltonian of interacting electrons the effective self-energy acting on electrons residing in a subspace of the full Hilbert space is derived. This subspace may correspond to, for example, partially filled narrow bands, which often characterize strongly correlated materials. The formalism delivers naturally the frequency-dependent effective interaction (the Hubbard U) and provides a general framework for constructing theoretical models based on the Green's function language. It also furnishes a general scheme for first-principles calculations of complex systems in which the main correlation effects are concentrated on a small subspace of the full Hilbert space.

Selenium status of low-selenium area residents: Polish experience.

The concentration of selenium (Se) in human organism varies widely between geographical areas depending on its content in soil and plants, dietary Se intake, bioavailability and retention, mineral interactions and other factors. The study includes healthy inhabitants of different regions of Poland; pregnant women, lactating women, children from 0 to 15 years of age and adults. Systematic determinations allow us to observe changes of the concentration of Se in time, which may be significant for developing preventive action. The results obtained confirm our thesis that Se concentration in the blood of the inhabitants of Poland depends on the region of the country. In recent years, in a considerable number of Polish inhabitants, the concentration of Se in blood plasma has been relatively low-about 50-55 microg/l, and the calculated daily dietary intake about 30-40 microg/day. The low levels of the element in the blood and urine are probably due to its deficiency in the diet.

Comparison of gravimetry and hydrolysis/derivatization/gas chromatography-mass spectrometry for quantitative analysis of fat from standard reference infant formula powder using supercritical fluid extraction.

This paper describes a comparative study of the gravimetric versus hydrolysis/derivatization/gas chromatography-mass spectrometry determination of fat in infant formula. Fat was extracted using supercritical carbon dioxide modified with a small amount of ethanol, the extract was weighed, and the total fat was determined gravimetrically. Subsequently, another sample of the supercritical fluid fat extract was hydrolyzed to yield free fatty acids, which were converted to their methyl ester derivatives (FAMEs). Quantification was performed by GC-MS. NIST Standard Reference Material (SRM-1846) was used to validate both fat determination methods. Results showed that the gravimetric average percent fat was 26.86%, whereas the GC-MS method yielded 24.64%. Some peaks were detected in the ion chromatogram from the GC-MS that were identified as nonfatty acids such as aldehydes, which may account for the higher percentage fat measured as weight of extract rather than measured as FAMEs expressed as triglycerides.

Tay-Sachs screening in the Jewish Ashkenazi population: DNA testing is the preferred procedure.

A unique screening program for the identification of Tay-Sachs Disease (TSD) heterozygotes has been performed in the tradi- tional Orthodox Ashkenazi Jewish (AJ) community since 1983. In recent years the program has utilized the biochemical assay for the determination of hexosaminidase A levels by the heat inactivation technique as well as by direct DNA analysis. The three mutations which were analyzed were those that have been shown to be prevalent among AJ TSD patients and carriers, namely the four nucleotide insertion mutation in exon 11 (1278+TATC), the splice mutation at the 5' end of intron 12 (1421+1g-->c), and the adult mutation, a Gly(269)-->Ser substitution in exon 5 (G269S). A total of 103,133 individuals were tested by biochemical analysis, and 38,197 of them were also assayed by DNA testing. Furthermore, 151 chromosomes from TSD patients or obligate heterozygotes were subjected to DNA analysis for one of the three mutations. DNA testing of the latter identified one of the three AJ mutations in every case, predicting a very high detection rate of heterozygotes in this community by this method. By contrast, the sensitivity of the enzyme assay ranged from 93.1% to 99.1% depending on the exclusion (inclusion) of inconclusive results as positive, while the specificity ranged from 88.1% to 98.8% depending on the inclusion (exclusion) of inconclusive results as positive. Our results strongly support the use of DNA testing alone as the most cost-effective and efficient approach to carrier screening for TSD in individuals of confirmed Ashkenazi Jewish ancestry.

Diphtheria toxin A gene-mediated HIV-1 protection of cord blood-derived T cells in the SCID-hu mouse model.

The reconstitutive potential of CD34+-derived cord blood (CB) cells, transduced with a regulated diphtheria toxin A (DT-A) chain gene, was examined in SCID-hu mice harboring a conjoint organ composed of human thymus and liver (thy/liv). The DT-A-transduced cells, injected directly into the thy/liv organ, showed the same engraftment potential as control CB cells transduced with the non-DT-A parental vector. CB cells, distinguishable from the thy/liv cells by the HLA marker B7, were preferentially maintained in ex vivo culture. In the thy/liv organ, the engrafted CB cells represented >80% of the total cells. A majority of cells (>70%) in the thy/liv organ were also CD4+CD8+, as would be expected of maturing thymocytes. The incidence of double-positive cells was highest at 44 days (compared with 30 days and 80 days) after injection of CB cells. This suggested that a minimum time was required to achieve optimal proliferation of cells in the thy/liv organ but that, at later times, all of the early cells had matured. Thus, the population used for engraftment contained early cells but not self-renewing cells. The double-positive cells matured rapidly into single-positive cells (either CD4+ or CD8+) when placed in ex vivo culture. Marked cells (neo+) could readily be detected in the thy/liv-derived cells. The cells transduced with DT-A showed long-term protection in ex vivo culture against HIV T lymphotropic isolate NL4-3. This study shows that DT-A-transduced cells had no apparent disadvantage in engraftment of the thy/liv organ and did not have any toxic effects in vivo. Such cells were protected against HIV infection even when challenged more than 2 months after transduction and after a 44-day engraftment period in the thy/liv mice. These data support the feasibility of toxin gene therapy as a strategy for HIV infection.

HIV-gp120 induced cell death in hematopoietic progenitor CD34+ cells.

Haematologic abnormalities accompany the majority of HIV-1 infections. At present it is unclear whether this is due directly to HIV infection of hematopoietic progenitor cells, or whether this results from an indirect mechanism secondary to HIV infection. Here we provide evidence for an indirect mechanism, whereby hematopoietic progenitor cells undergo HIV gp120-induced apoptosis (programmed cell death) even in the absence of HIV infection. Freshly isolated, purified human hematopoietic progenitor CD34+ cells, derived from both umbilical cord blood and bone marrow, co-expressed the CD4 marker at low density on their surface. Although these CD34+CD4+ cells theoretically should be capable of productive infection by HIV, we found that HIV-IIIB could not establish productive infection in these cells. Nonetheless, gp120 from IIIB could bind the cells. Thus, binding of gp120 did not correlate with infectivity. Furthermore, binding of gp120 was a specific event, leading to apoptosis upon crosslinking with anti-gp120 through a fas-dependent mechanism. If apoptosis is also observed in vivo even in uninfected hematopoietic cells, this could contribute significantly to the impairment in hematopoietic cell number and function. Our data suggest a novel indirect mechanism for depletion of CD34+ and CD34+-derived cells even in the absence of productive viral infection of these cells.

Comparison of retroviral-mediated gene transfer into cultured human CD34+ hematopoietic progenitor cells derived from peripheral blood, bone marrow, and fetal umbilical cord blood.

Genetic alteration of stem cells ex vivo followed by bone marrow transplantation could potentially be used in the treatment of numerous diseases and malignancies. However, there are many unanswered questions as to the best source of hematopoietic cells for long-term reengraftment and the most effective way to introduce foreign genes into this target cell. We have compared retroviral-mediated gene transfer into CD34+-enriched cells derived from peripheral blood (PB), bone marrow (BM), or fetal umbilical cord blood (CB). Cells from all three sources that had been expanded ex vivo in the presence of stem cell factor (SCF), interleukin-3 (IL-3), IL-6, and granulocyte colony-stimulating factor (G-CSF) showed transduction efficiencies ranging from 5-45%, as measured by acquisition of G418 resistance. The average efficiencies of gene transfer from multiple experiments for PB, BM, and CB were not statistically different. To determine the effect of ex vivo expansion on gene transfer into CB CD34+ cells, we compared the transduction efficiencies of cells exposed to virus immediately after harvest and CD34 selection or after 6 days of culture CD34+ CB cells were more effectively transduced after expansion in culture, showing gene transfer efficiencies 3- to 5-fold higher on day 6 compared with day 0. Last, we examined retroviral transduction via spinoculation of CB CD34+ cells and found it to be approximately as effective as our standard transduction with no significant loss of cell viability as measured by colony formation in semi-solid medium.

Heterozygosity for Tay-Sachs disease in non-Jewish Americans with ancestry from Ireland or Great Britain.

We performed a genetic epidemiological analysis of American non-Jewish people with ancestry from Ireland or Great Britain with regard to heterozgosity for Tay-Sachs disease (TSD). This study was prompted by a recent report that the frequency of heterozygosity for TSD among Irish Americans was 1 in 8, a frequency much higher than that recognised for any other population group. We identified 19 of 576 (3.3%) people of Irish background as TSD heterozygotes by the standard thermolability assay for beta-hexosaminidase A (Hex A) activity. Three of 289 people of non-Irish British Isles background (1%) were also identified as heterozygotes by biochemical testing. Specimens from the biochemically identified Irish heterozygotes were analysed for seven different Hex A alpha subunit gene mutations; three (15.8%) had a lethal +1 IVS-9 G to A mutation, previously noted to be a common mutation among TSD heterozygotes of Irish ancestry. Eight of 19 (42.1%) had one of two benign or pseudodeficiency mutations, and no mutation was found in 42.1% of the heterozygotes analysed. These data indicate that non-Jewish Americans with Irish background have a significantly increased frequency of heterozygosity at the Hex A alpha subunit gene locus, but that approximately 42% of the biochemically ascertained heterozygotes have clinically benign mutations. A pseudodeficiency mutation was identified in one of the three TSD heterozygotes of non-Irish British Isles background; no mutations were found in the other two. The data allow for a frequency estimate of deleterious alleles for TSD among Irish Americans of 1 in 192 to 1 in 52. Non-Jewish Americans with ancestry from Great Britain have a minimal, if any, increase in rate of heterozygosity at the TSD gene locus relative to the general population.

Increased urinary nitrite excretion in children with minimal change nephrotic syndrome.

OBJECTIVE: We tested the hypothesis that nitric oxide synthesis by the kidney is increased in children with primary nephrotic syndrome. METHODS: We examined the urinary excretion of nitrite, a stable metabolite of nitric oxide, using the Griess reaction, in children with nephrotic syndrome. RESULTS: In comparison with healthy children, patients with minimal change nephrotic syndrome had increased urinary nitrite excretion regardless of whether the disease was in relapse or remission (p < 0.025). In contrast, urinary nitrite excretion was similar in control subjects and patients with focal segmental glomerulosclerosis or IgA nephropathy. CONCLUSION: These findings indicate that measurement of urinary nitrite excretion may be a useful test to help discriminate between minimal change nephrotic syndrome and focal segmental glomerulosclerosis in children with idiopathic nephrotic syndrome.

Optimization of gene transfer using cationic lipids in cell lines and primary human CD4+ and CD34+ hematopoietic cells.

Cationic lipids offer several advantages for gene delivery, both in vitro and in vivo. However, high-efficiency gene transfer has been demonstrated only for limited cell types. Here, we examine the level of expression of a luciferase reporter gene, delivered using cationic lipids, in both cell lines and primary human cells including peripheral blood mononuclear cells and CD34(+)-enriched hematopoietic cells. Variables shown to affect the efficiency of gene expression included the type of lipid, the amounts of DNA and lipid, the day of assay following transfection, the media used for lipid:DNA complex formation, the cell number, the promoter driving expression of the reporter gene and the physiological state of the cells (e.g., whether or not cells were differentiated). The maximal luciferase expression observed with the primary cells was one to two orders of magnitude lower than that seen in cell lines. Further studies, possibly involving altering the growth conditions for the cells, or using episomal vectors that will allow extrachromosomal maintenance of the DNA, are required to improve the level of transgene expression in the primary human cell types used here.

An intraventricular axial flow blood pump integrated with a bearing purge system.

The future development of implantable axial flow blood pumps must address two major issues: mechanically induced hemolysis and shaft seal reliability. The recent revisions to our miniature intraventricular axial flow left ventricular assist device (LVAD) were aimed particularly at addressing these concerns. To improve hemocompatibility, a new impeller has been designed according to the following criteria: 1) gradual pressure rise along the blade chord; 2) minimized local fluid acceleration to prevent cavitation; 3) minimum surface roughness; and 4) radius edges. Subsequent in vitro hemolysis tests conducted with bovine and ovine blood have demonstrated very low hemolysis (normalized index of hemolysis = 0.0051 +/- 0.0047 g/100 L) with this new impeller design. To address the need for a reliable seal, we have developed a purged seal system consisting of a miniature lip seal and ceramic pressure groove journal bearing that also acts as a purge pump. Several spiral grooves formed on the bearing surface provide viscous pumping of the purge fluid, generating more than 3,000 mmHg at 10,000 rpm. This purge flow flushes the lip seal and prevents blood backflow into the bearing. We have found this purge pump to offer several advantages because it is simple, compact, durable, does not require separate actuation, and offers a wide range of flow, depending upon the groove design. In vivo animal tests demonstrated the potential of the purged seal system.

An improved left ventricular cannula for chronic dynamic blood pump support.

Ventricular unloading with dynamic blood pumps can be markedly affected by the geometry of the cannula tip within the ventricular chamber. Due to the ability of these pumps to develop significant negative inflow pressure, existing cannula tips designed for passively filling blood pumps can be predisposed to inflow occlusion by intraventricular anatomic structures. A novel "trumpet" mouth cannula was constructed to overcome this limiting problem. This design was based on two criteria: to provide additional stenting to the ventricular apex, and to assure placement of the tip opening relative to the endocardial surface. This prototype cannula was evaluated in vivo against conventional caged, blunt, and tapered designs to assess anatomic and hemodynamic interaction within the ventricular apex. Post mortem examination revealed the inflow tract to be devoid of myocardial obstruction in all cases. These initial studies indicate that a trumpet mouth cannula can provide satisfactory hemodynamic performance required by dynamic blood pumps.

Homozygous type I protein C deficiency in two unrelated families exhibiting thrombophilia related to Ala136-->Pro or Arg286-->His mutations.

Separate single nucleotide mutations have been identified in two unrelated homozygous type I protein C deficient individuals suffering from thrombophilia. Each mutation, initially established by direct DNA sequencing of polymerase chain reaction amplification products, results in an amino acid substitution. The first mutation (PCClamart) results in an Ala136 to Pro substitution in the protein's second epidermal growth factor-like domain. The second mutation (PCMünchen) results in an Arg286 to His substitution in the serine protease domain. Comparison of the location of these two mutations and the relative conservation of the two regions in homologous vitamin K-dependent plasma proteins is consistent with the difference in severity of protein C deficiency and disease in the two individuals. Both mutations result in the abolition of a naturally occurring restriction endonuclease site, thereby allowing independent confirmation of the mutations and rapid and unambiguous genetic analysis of protein C deficiency in family members. In both families, the genetic analysis has proven useful in cases where an assignment of the protein C status based upon clinical laboratory measurements was either ambiguous or incorrect.

Genetic analysis of a large kindred exhibiting type I protein C deficiency and associated thrombosis.

A previously described large Vermont kindred possessing a high incidence of venous thromboembolism with associated Type I protein C deficiency (1) has been genetically analyzed. All nine exons of the protein C gene, including both coding and non-coding regions, have been amplified from blood cell genomic DNA using the Tag DNA polymerase chain reaction (PCR) and primers corresponding to flanking intronic regions, and the products directly sequenced. An initial mutation (C-->T) resulting in Thr298-->Met was observed in one arm of the family exhibiting a history of thrombosis and protein C deficiency and was designated protein CVERMONT IIa. However, examination of the kindred member parent (male) of this arm and members of other arms of the kindred demonstrated that the mutation entered the arm via the genetically unrelated spouse. Further analysis of the father and members of other arms of the kindred revealed a different mutation (C insertion: CAT-->CCAT), resulting in a frameshift beginning at amino acid #107 (His-->Pro) and truncation of the protein at codon #119 of the mature protein. This mutation, called protein CVERMONT IIb, is associated with protein C deficiency and thrombosis throughout the kindred.

Protein CVermont: symptomatic type II protein C deficiency associated with two GLA domain mutations.

This study investigates type II protein C deficiency in a family with manifestations of both arterial and venous thrombosis. Of 64 members of the kindred, 14 have been tested and 7 have PC deficiency. Among affected individuals (n = 7), mean protein C levels by different assays were as follows: enzyme-linked immunosorbent assay (ELISA), 3.8 micrograms/mL (2.1 to 4.3 micrograms/mL); amidolytic with venom activator, 115% (60% to 140%); clotting with venom activator, 42% (23% to 59%). The mean ratio of clotting to amidolytic assays for the affected individuals was 0.37 compared with a normal range of 0.8 to 1.2. Thus, the affected individuals have normal total protein C and their activated protein C has a normal active site assessed by chromogenic substrate; however, they have markedly diminished clotting activity. Immunoassay and chromatography data suggested an abnormality of carboxylation in the gamma carboxyglutamic acid (Gla) domain. Polymerase chain reaction amplification and direct DNA sequencing of exon 2 from genomic DNA of affected individuals showed two nucleotide substitutions. One of the mutations (A----C) results in Glu20----Ala, thereby eliminating a site for vitamin K-dependent gamma-carboxylation. The other substitution (G----A) results in a Val34----Met mutation. DNA sequencing of the other exons from affected individuals has shown no further difference from that of the wild-type gene. The former mutation also removes a Bgl II restriction endonuclease site, which has allowed us to confirm the mutation in affected individuals by direct digestion and Southern hybridization of genomic DNA from family members. This is the first reported family with documented Gla domain mutations in the protein C gene.