Objectives
Amyloid‐beta (Aβ) and tau pathologies are commonly observed among clinically normal older individuals at postmortem and can now be detected with in vivo neuroimaging. The association and ...interaction of these proteinopathies with prospective cognitive decline in normal aging and preclinical Alzheimer's disease (AD) remains to be fully elucidated.
Methods
One hundred thirty‐seven older individuals (age = 76.3 ± 6.22 years) participating in the Harvard Aging Brain Study underwent Aβ (11C‐Pittsburgh compound B) and tau (18F‐flortaucipir) positron emission tomography (PET) with prospective neuropsychological assessments following PET imaging (mean number of cognitive visits = 2.8 ± 1.1). Tau and Aβ PET measures were assessed in regions of interest (ROIs) as well as vertex‐wise map analyses. Cognitive change was evaluated with Memory and Executive Function composites.
Results
Higher levels of Aβ and tau were both associated with greater memory decline, but not with change in executive function. Higher cortical Aβ was associated with higher tau levels in all ROIs, independent of age, and very elevated levels of tau were observed primarily in clinically normal with elevated Aβ. A significant interaction between tau and Aβ was observed in both ROI and map‐level analyses, such that rapid prospective memory decline was observed in participants who had high levels of both pathologies.
Interpretation
Our results are consistent with the supposition that both Aβ and tau are necessary for memory decline in the preclinical stages of AD. These findings may be relevant for disambiguating aging and early cognitive manifestations of AD, and to inform secondary prevention trials in preclinical AD. Ann Neurol 2019;00:1–3 ANN NEUROL 2019;85:181–193.
Band engineering is an effective strategy to improve the electronic transport properties of semiconductors. In thermoelectric materials research, density‐of‐states effective mass is an undoubted key ...factor in verifying the band engineering effect and establishing a strategy for enhancing thermoelectric performance. However, estimation of the effective mass is demanding or inaccurate depending on the methods taken. A simple equation is proposed, valid for all degeneracy: Log10 (md*T/300) = (2/3) Log10 (n) − (2/3) 20.3 − (0.00508 × |S|) + (1.58 × 0.967|S|) that utilizes experimentally determined Seebeck coefficient (S) and carrier concentration (n) to determine the effective mass (md*) at a temperature (T). This straightforward equation, which gives an accurate analysis of the band modulation in terms of md*, is indispensable in designing thermoelectric materials of maximized performance.
The density‐of‐states (DOS) effective mass of thermoelectric materials can be estimated accurately with the single parabolic band model. However due to complex Fermi integral calculations involved, an equation that is valid in degenerate materials is instead utilized erroneously. This work proposes another simple, universal, and accurate equation that can be used for any degeneracy to determine the DOS effective mass.
Objective
Neuropathological studies have demonstrated that cerebrovascular disease and Alzheimer disease (AD) pathology frequently co‐occur in older adults. The extent to which cerebrovascular ...disease influences the progression of AD pathology remains unclear. Leveraging newly available positron emission tomography (PET) imaging, we examined whether a well‐validated measure of systemic vascular risk and β‐amyloid (Aβ) burden have an interactive association with regional tau burden.
Methods
Vascular risk was quantified at baseline in 152 clinically normal older adults (mean age = 73.5 ± 6.1 years) with the office‐based Framingham Heart Study cardiovascular disease risk algorithm (FHS‐CVD). We acquired Aβ (11C‐Pittsburgh compound B) and tau (18F‐flortaucipir) PET imaging on the same participants. Aβ PET was performed at baseline; tau PET was acquired on average 2.98 ± 1.1 years later. Tau was measured in the entorhinal cortex (EC), an early site of tau deposition, and in the inferior temporal cortex (ITC), an early site of neocortical tau accumulation associated with AD. Linear regression models examined FHS‐CVD and Aβ as interactive predictors of tau deposition, adjusting for age, sex, APOE ε4 status, and the time interval between baseline and the tau PET scan.
Results
We observed a significant interaction between FHS‐CVD and Aβ burden on subsequently measured ITC tau (p < 0.001), whereby combined higher FHS‐CVD and elevated Aβ burden was associated with increased tau. The interaction was not significant for EC tau (p = 0.16).
Interpretation
Elevated vascular risk may influence tau burden when coupled with high Aβ burden. These results suggest a potential link between vascular risk and tau pathology in preclinical AD. Ann Neurol 2019; 1–8 ANN NEUROL 2019;85:272–279.
Complexity of holographic superconductors Yang, Run-Qiu; Jeong, Hyun-Sik; Niu, Chao ...
The journal of high energy physics,
04/2019, Letnik:
2019, Številka:
4
Journal Article
Recenzirano
Odprti dostop
A
bstract
We study the complexity of holographic superconductors (Einstein-Maxwell-complex scalar actions in
d
+ 1 dimension) by the “complexity = volume” (CV) conjecture. First, it seems that there ...is a universal property: the superconducting phase always has a smaller complexity than the unstable normal phase below the critical temperature, which is similar to a free energy. We investigate the temperature dependence of the complexity. In the low temperature limit, the complexity (of formation) scales as
T
α
, where α is a function of the complex scalar mass
m
2
, the U(1) charge
q
, and dimension
d
. In particular, for
m
2
= 0, we find
α
=
d
−1, independent of
q
, which can be explained by the near horizon geometry of the low temperature holographic superconductor. Next, we develop a general numerical method to compute the
time-dependent
complexity by the CV conjecture. By this method, we compute the time-dependent complexity of holographic superconductors. In both normal and superconducting phase, the complexity increases as time goes on and the growth rate saturates to a temperature dependent constant. The higher the temperature is, the bigger the growth rate is. However, the growth rates do not violate the Lloyd’s bound in all cases and saturate the Lloyd’s bound in the high temperature limit at a late time.
Tau and amyloid beta (Aβ) proteins accumulate along neuronal circuits in Alzheimer's disease. Unraveling the genetic background for the regional vulnerability of these proteinopathies can help in ...understanding the mechanisms of pathology progression. To that end, we developed a novel graph theory approach and used it to investigate the intersection of longitudinal Aβ and tau positron emission tomography imaging of healthy adult individuals and the genetic transcriptome of the Allen Human Brain Atlas. We identified distinctive pathways for tau and Aβ accumulation, of which the tau pathways correlated with cognitive levels. We found that tau propagation and Aβ propagation patterns were associated with a common genetic profile related to lipid metabolism, in which APOE played a central role, whereas the tau-specific genetic profile was classified as 'axon related' and the Aβ profile as 'dendrite related'. This study reveals distinct genetic profiles that may confer vulnerability to tau and Aβ in vivo propagation in the human brain.
Flat metasurfaces with subwavelength meta‐atoms can be designed to manipulate the electromagnetic parameters of incident light and enable unusual light–matter interactions. Although hydrogel‐based ...metasurfaces have the potential to control optical properties dynamically in response to environmental conditions, the pattern resolution of these surfaces has been limited to microscale features or larger, limiting capabilities at the nanoscale, and precluding effective use in metamaterials. This paper reports a general approach to developing tunable plasmonic metasurfaces with hydrogel meta‐atoms at the subwavelength scale. Periodic arrays of hydrogel nanodots with continuously tunable diameters are fabricated on silver substrates, resulting in humidity‐responsive surface plasmon polaritons (SPPs) at the nanostructure–metal interfaces. The peaks of the SPPs are controlled reversibly by absorbing or releasing water within the hydrogel matrix, the matrix‐generated plasmonic color rendering in the visible spectrum. This work demonstrates that metasurfaces designed with these spatially patterned nanodots of varying sizes benefit applications in anti‐counterfeiting and generate multicolored displays with single‐nanodot resolution. Furthermore, this work shows system versatility exhibited by broadband beam‐steering on a phase modulator consisting of hydrogel supercell units in which the size variations of constituent hydrogel nanostructures engineer the wavefront of reflected light from the metasurface.
This paper reports an approach for plasmonic metasurfaces with hydrogel meta‐atoms at the subwavelength scale. Periodic arrays of hydrogel nanodots with tunable diameters are fabricated on silver substrates, resulting in humidity‐responsive surface plasmon polaritons. This work demonstrates that metasurfaces designed with spatially patterned hydrogel nanodots of varying size distributions benefit applications in anti‐counterfeiting, multicolored displays, and a phase modulator.
Objective
Elevated vascular risk and beta‐amyloid (Aβ) burden have been synergistically associated with cognitive decline in preclinical Alzheimer's disease (AD), although the underlying mechanisms ...remain unclear. We examined whether accelerated longitudinal tau accumulation mediates the vascular risk‐Aβ interaction on cognitive decline.
Methods
We included 175 cognitively unimpaired older adults (age 70.5 ± 8.0 years). Baseline vascular risk was quantified using the office‐based Framingham Heart Study general cardiovascular disease risk score (FHS‐CVD). Baseline Aβ burden was measured with Pittsburgh Compound‐B positron emission tomography (PET). Tau burden was measured longitudinally (3.6 ± 1.5 years) with Flortaucipir PET, focusing on inferior temporal cortex (ITC). Cognition was assessed longitudinally (7.0 ± 2.0 years) using the Preclinical Alzheimer's Cognitive Composite. Linear mixed effects models examined the interactive effects of baseline vascular risk and Aβ on longitudinal ITC tau. Additionally, moderated mediation was used to determine whether tau accumulation mediated the FHS‐CVD*Aβ effect on cognitive decline.
Results
We observed a significant interaction between elevated baseline FHS‐CVD and Aβ on greater ITC tau accumulation (p = 0.004), even in individuals with Aβ burden below the conventional threshold for amyloid positivity. Examining individual vascular risk factors, we found elevated systolic blood pressure and body mass index showed independent interactions with Aβ on longitudinal tau (both p < 0.0001). ITC tau accumulation mediated 33% of the interactive association of FHS‐CVD and Aβ on cognitive decline.
Interpretation
Vascular risks interact with subthreshold levels of Aβ to promote cognitive decline, partially by accelerating early neocortical tau accumulation. Our findings support vascular risk reduction, especially treating hypertension and obesity, to attenuate Aβ‐related tau pathology and reduce late‐life cognitive decline. ANN NEUROL 2022;92:745–755
The widespread use of thermoelectric technology is constrained by a relatively low conversion efficiency of the bulk alloys, which is evaluated in terms of a dimensionless figure of merit (zT). The ...zT of bulk alloys can be improved by reducing lattice thermal conductivity through grain boundary and point-defect scattering, which target low- and high-frequency phonons. Dense dislocation arrays formed at low-energy grain boundaries by liquid-phase compaction in Bi0.5Sb1.5Te3 (bismuth antimony telluride) effectively scatter midfrequency phonons, leading to a substantially lower lattice thermal conductivity. Full-spectrum phonon scattering with minimal charge-carrier scattering dramatically improved the zT to 1.86 ± 0.15 at 320 kelvin (K). Further, a thermoelectric cooler confirmed the performance with a maximum temperature difference of 81 K, which is much higher than current commercial Peltier cooling devices.
The availability of blood-based assays detecting Alzheimer's disease (AD) pathology should greatly accelerate AD therapeutic development and improve clinical care. This is especially true for markers ...that capture the risk of decline in pre-symptomatic stages of AD, as this would allow one to focus interventions on participants maximally at risk and at a stage prior to widespread synapse loss and neurodegeneration. Here we quantify plasma concentrations of an N-terminal fragment of tau (NT1) in a large, well-characterized cohort of clinically normal elderly who were followed longitudinally. Plasma NT1 levels at study entry (when all participants were unimpaired) were highly predictive of future cognitive decline, pathological tau accumulation, neurodegeneration, and transition to a diagnosis of MCI/AD. These predictive effects were particularly strong in participants with even modestly elevated brain β-amyloid burden at study entry, suggesting plasma NT1 levels capture very early cognitive, pathologic and neurodegenerative changes along the AD trajectory.
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