58 research outputs found
The Field-Tuned Superconductor-Insulator Transition with and without Current Bias
The magnetic-field-tuned superconductor-insulator transition has been studied
in ultrathin Beryllium films quench-condensed near 20 K. In the zero-current
limit, a finite-size scaling analysis yields the scaling exponent product vz =
1.35 +/- 0.10 and a critical sheet resistance R_{c} of about 1.2R_{Q}, with
R_{Q} = h/4e^{2}. However, in the presence of dc bias currents that are smaller
than the zero-field critical currents, vz becomes 0.75 +/- 0.10. This new set
of exponents suggests that the field-tuned transitions with and without dc bias
currents belong to different universality classes.Comment: RevTex 4 pages, 4 figures, and 1 table minor change
Microtesla MRI of the human brain combined with MEG
One of the challenges in functional brain imaging is integration of
complementary imaging modalities, such as magnetoencephalography (MEG) and
functional magnetic resonance imaging (fMRI). MEG, which uses highly sensitive
superconducting quantum interference devices (SQUIDs) to directly measure
magnetic fields of neuronal currents, cannot be combined with conventional
high-field MRI in a single instrument. Indirect matching of MEG and MRI data
leads to significant co-registration errors. A recently proposed imaging method
- SQUID-based microtesla MRI - can be naturally combined with MEG in the same
system to directly provide structural maps for MEG-localized sources. It
enables easy and accurate integration of MEG and MRI/fMRI, because microtesla
MR images can be precisely matched to structural images provided by high-field
MRI and other techniques. Here we report the first images of the human brain by
microtesla MRI, together with auditory MEG (functional) data, recorded using
the same seven-channel SQUID system during the same imaging session. The images
were acquired at 46 microtesla measurement field with pre-polarization at 30
mT. We also estimated transverse relaxation times for different tissues at
microtesla fields. Our results demonstrate feasibility and potential of human
brain imaging by microtesla MRI. They also show that two new types of imaging
equipment - low-cost systems for anatomical MRI of the human brain at
microtesla fields, and more advanced instruments for combined functional (MEG)
and structural (microtesla MRI) brain imaging - are practical.Comment: 8 pages, 5 figures - accepted by JM
Quantum critical points with the Coulomb interaction and the dynamical exponent: when and why z=1
A general scenario that leads to Coulomb quantum criticality with the
dynamical critical exponent z=1 is proposed. I point out that the long-range
Coulomb interaction and quenched disorder have competing effects on z, and that
the balance between the two may lead to charged quantum critical points at
which z=1 exactly. This is illustrated with the calculation for the Josephson
junction array Hamiltonian in dimensions D=3-\epsilon. Precisely in D=3,
however, the above simple result breaks down, and z>1. Relation to other
theoretical studies is discussed.Comment: RevTex, 4 pages, 1 ps figur
Superconducting zero temperature phase transition in two dimensions and in the magnetic field
We derive the Ginzburg-Landau-Wilson theory for the superconducting phase
transition in two dimensions and in the magnetic field. Without disorder the
theory describes a fluctuation induced first-order quantum phase transition
into the Abrikosov lattice. We propose a phenomenological criterion for
determining the transition field and discuss the qualitative effects of
disorder. Comparison with recent experiments on MoGe films is discussed.Comment: 7 pages, 2 figure
Spin-Polarized Transport Across an LaSrMnO/YBaCuO Interface: Role of Andreev Bound States
Transport across an
LaSr_{3}/YBa_{3}_{7}_{3}$/YBCO and Ag/YBCO. In all cases, YBCO is used as bottom layer to
eliminate the channel resistance and to minimize thermal effects. The observed
differential conductance re ects the role of Andreev bound states in a-b
planes, and brings out for the first time the suppression of such states by the
spin-polarized transport across the interface. The theoretical analysis of the
measured data reveals decay of the spin polarization near the LSMO surface with
temperature, consistent with the reported photoemission data.Comment: 5 pages LaTeX, 3 eps figures included, accepted by Physical Review
Granulated superconductors:from the nonlinear sigma model to the Bose-Hubbard description
We modify a nonlinear sigma model (NLSM) for the description of a granulated
disordered system in the presence of both the Coulomb repulsion and the Cooper
pairing. We show that under certain controlled approximations this model is
reduced to the Bose-Hubbard (or ``dirty-boson'') model with renormalized
coupling constants. We obtain a more general effective action (which is still
simpler than the full NLSM action) which can be applied in the region of
parameters where the reduction to the Bose-Hubbard model is not justified. This
action may lead to a different picture of the superconductor-insulator
transition in 2D systems.Comment: 4 pages, revtex, no figure
The Period Changes of the Cepheid RT Aurigae
Observations of the light curve for the 3.7-day Cepheid RT Aur both before
and since 1980 indicate that the variable is undergoing an overall period
increase, amounting to +0.082 +-0.012 s/yr, rather than a period decrease, as
implied by all observations prior to 1980. Superposed on the star's O-C
variations is a sinusoidal trend that cannot be attributed to random
fluctuations in pulsation period. Rather, it appears to arise from light travel
time effects in a binary system. The derived orbital period for the system is P
= 26,429 +-89 days (72.36 +-0.24 years). The inferred orbital parameters from
the O-C residuals differ from those indicated by existing radial velocity data.
The latter imply the most reasonable results, namely a1 sin i = 9.09 (+-1.81) x
10^8 km and a minimum secondary mass of M2 = 1.15 +-0.25 Msun. Continued
monitoring of the brightness and radial velocity changes in the Cepheid are
necessary to confirm the long-term trend and to provide data for a proper
spectroscopic solution to the orbit.Comment: Accepted for publication in PASP (November 2007
Spintronics: Fundamentals and applications
Spintronics, or spin electronics, involves the study of active control and
manipulation of spin degrees of freedom in solid-state systems. This article
reviews the current status of this subject, including both recent advances and
well-established results. The primary focus is on the basic physical principles
underlying the generation of carrier spin polarization, spin dynamics, and
spin-polarized transport in semiconductors and metals. Spin transport differs
from charge transport in that spin is a nonconserved quantity in solids due to
spin-orbit and hyperfine coupling. The authors discuss in detail spin
decoherence mechanisms in metals and semiconductors. Various theories of spin
injection and spin-polarized transport are applied to hybrid structures
relevant to spin-based devices and fundamental studies of materials properties.
Experimental work is reviewed with the emphasis on projected applications, in
which external electric and magnetic fields and illumination by light will be
used to control spin and charge dynamics to create new functionalities not
feasible or ineffective with conventional electronics.Comment: invited review, 36 figures, 900+ references; minor stylistic changes
from the published versio
БИФИДОГЕННЫЕ СВОЙСТВА БИОТЕХНОЛОГИЧЕСКОГО АНАЛОГА ЛАКТОФЕРРИНА ЧЕЛОВЕКА
Background: Recent research shows that the growth and development of the gastrointestinal tract of children fed by breast milk is more intense than that of the formula fed, since the human lactoferrin contained in the breast milk is a factor that stimulates cell growth. Therefore, the possibility of using exogenous lactoferrin will be of great importance in the nutrition of infants.Objektive: To study the bifidogenic properties of the biotechnological analogue of human lactoferrin. Methods: Kinetics of growth and CFU titer of bifidobacterial culture in the presence of a biotechnological analogue of human lactoferrin (0,05–5 mg /ml) was determined.Results: It has been shown that different concentrations of the protein can have both a stimulating (for B. bifidum and B. infantis) and inhibitory (for B. longum) effect on the growth of bifidobacteria, which is due to the affinity of lactoferrin binding to them. It seems important to further study the stimulating effect of this protein on the growth of lactobacilli in the intestine of the child.Conclusion: Due to bifidogenic and high bactericidal action, lactoferrin can be effective in feeding newborns.Обоснование. Новейшие исследования показывают, что рост и развитие желудочно-кишечного тракта детей, вскармливаемых материнским молоком, происходит интенсивнее, чем у вскармливаемых молочными смесями, поскольку содержащийся в нем лактоферрин человека является фактором, стимулирующим клеточный рост. Именно поэтому возможность использования экзогенного лактоферрина будет иметь большую значимость в питании грудных детей.Цель исследования — изучить бифидогенные свойства биотехнологического аналога лактоферрина человека.Методы. Определялась кинетика роста и КОЕ-титр культивирования бифидобактерий в присутствии биотехнологического аналога лактоферрина человека.Результаты. Показано, что различные концентрации данного белка (0,05–5 мг/мл) могут оказывать как стимулирующее (для Bifidobacterium bifidum и Bifidobacterium infantis), так и ингибирующее (для Bifidobacterium longum) действие в отношении роста бифидобактерий, что обусловлено аффинностью связывания с ними лактоферрина. Представляется важным дальнейшее изучение стимулирующего эффекта этого белка на рост лактобацилл в кишечнике ребенка.Заключение. Благодаря бифидогенному и выраженному бактерицидному действию лактоферрин может быть использован в лечебном питании новорожденных
Soluble TREM2 in CSF and its association with other biomarkers and cognition in autosomal-dominant Alzheimer's disease: a longitudinal observational study
BACKGROUND: Therapeutic modulation of TREM2-dependent microglial function might provide an additional strategy to slow the progression of Alzheimer's disease. Although studies in animal models suggest that TREM2 is protective against Alzheimer's pathology, its effect on tau pathology and its potential beneficial role in people with Alzheimer's disease is still unclear. Our aim was to study associations between the dynamics of soluble TREM2, as a biomarker of TREM2 signalling, and amyloid β (Aβ) deposition, tau-related pathology, neuroimaging markers, and cognitive decline, during the progression of autosomal dominant Alzheimer's disease. METHODS: We did a longitudinal analysis of data from the Dominantly Inherited Alzheimer Network (DIAN) observational study, which includes families with a history of autosomal dominant Alzheimer's disease. Participants aged over 18 years who were enrolled in DIAN between Jan 1, 2009, and July 31, 2019, were categorised as either carriers of pathogenic variants in PSEN1, PSEN2, and APP genes (n=155) or non-carriers (n=93). We measured amounts of cleaved soluble TREM2 using a novel immunoassay in CSF samples obtained every 2 years from participants who were asymptomatic (Clinical Dementia Rating [CDR]=0) and annually for those who were symptomatic (CDR>0). CSF concentrations of Aβ40, Aβ42, total tau (t-tau), and tau phosphorylated on threonine 181 (p-tau) were measured by validated immunoassays. Predefined neuroimaging measurements were total cortical uptake of Pittsburgh compound B PET (PiB-PET), cortical thickness in the precuneus ascertained by MRI, and hippocampal volume determined by MRI. Cognition was measured using a validated cognitive composite (including DIAN word list test, logical memory delayed recall, digit symbol coding test [total score], and minimental status examination). We based our statistical analysis on univariate and bivariate linear mixed effects models. FINDINGS: In carriers of pathogenic variants, a high amyloid burden at baseline, represented by low CSF Aβ42 (β=–4·28 × 10^{–2} [SE 0·013], p=0·0012), but not high cortical uptake in PiB-PET (β=–5·51 × 10^{–3} [0·011], p=0·63), was the only predictor of an augmented annual rate of subsequent increase in soluble TREM2. Augmented annual rates of increase in soluble TREM2 were associated with a diminished rate of decrease in amyloid deposition, as measured by Aβ42 in CSF (r=0·56 [0·22], p=0·011), in presymptomatic carriers of pathogenic variants, and with diminished annual rate of increase in PiB-PET (r=–0·67 [0·25], p=0·0060) in symptomatic carriers of pathogenic variants. Presymptomatic carriers of pathogenic variants with annual rates of increase in soluble TREM2 lower than the median showed a correlation between enhanced annual rates of increase in p-tau in CSF and augmented annual rates of increase in PiB-PET signal (r=0·45 [0·21], p=0·035), that was not observed in those with rates of increase in soluble TREM2 higher than the median. Furthermore, presymptomatic carriers of pathogenic variants with rates of increase in soluble TREM2 above or below the median had opposite associations between Aβ42 in CSF and PiB-PET uptake when assessed longitudinally. Augmented annual rates of increase in soluble TREM2 in presymptomatic carriers of pathogenic variants correlated with decreased cortical shrinkage in the precuneus (r=0·46 [0·22]), p=0·040) and diminished cognitive decline (r=0·67 [0·22], p=0·0020). INTERPRETATION: Our findings in autosomal dominant Alzheimer's disease position the TREM2 response within the amyloid cascade immediately after the first pathological changes in Aβ aggregation and further support the role of TREM2 on Aβ plaque deposition and compaction. Furthermore, these findings underpin a beneficial effect of TREM2 on Aβ deposition, Aβ-dependent tau pathology, cortical shrinkage, and cognitive decline. Soluble TREM2 could, therefore, be a key marker for clinical trial design and interpretation. Efforts to develop TREM2-boosting therapies are ongoing
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