Crystallization in Ising quantum magnets Schauß, P.; Zeiher, J.; Fukuhara, T. ...
Science (American Association for the Advancement of Science),
03/2015, Letnik:
347, Številka:
6229
Journal Article
Recenzirano
Dominating finite-range interactions in many-body systems can lead to intriguing self-ordered phases of matter. For quantum magnets, Ising models with power-law interactions are among the most ...elementary systems that support such phases. These models can be implemented by laser coupling ensembles of ultracold atoms to Rydberg states. Here, we report on the experimental preparation of crystalline ground states of such spin systems. We observe a magnetization staircase as a function of the system size and show directly the emergence of crystalline states with vanishing susceptibility. Our results demonstrate the precise control of Rydberg many-body systems and may enable future studies of phase transitions and quantum correlations in interacting quantum magnets.
Quantum phases of matter are characterized by the underlying correlations of the many-body system. Although this is typically captured by a local order parameter, it has been shown that a broad class ...of many-body systems possesses a hidden nonlocal order. In the case of bosonic Mott insulators, the ground state properties are governed by quantum fluctuations in the form of correlated particle-hole pairs that lead to the emergence of a nonlocal string order in one dimension. By using high-resolution imaging of low-dimensional quantum gases in an optical lattice, we directly detect these pairs with single-site and single-particle sensitivity and observe string order in the one-dimensional case.
Correlation functions play an important role for the theoretical and experimental characterization of many-body systems. In solid-state systems, they are usually determined through scattering ...experiments, whereas in cold gases systems, time-of-flight, and in situ absorption imaging are the standard observation techniques. However, none of these methods allow the in situ detection of spatially resolved correlation functions at the single-particle level. Here, we give a more detailed account of recent advances in the detection of correlation functions using in situ fluorescence imaging of ultracold bosonic atoms in an optical lattice. This method yields single-site- and single-atom-resolved images of the lattice gas in a single experimental run, thus gaining direct access to fluctuations in the many-body system. As a consequence, the detection of correlation functions between an arbitrary set of lattice sites is possible. This enables not only the detection of two-site correlation functions but also the evaluation of non-local correlations, which originate from an extended region of the system and are used for the characterization of quantum phases that do not possess (quasi-)long-range order in the traditional sense.
Science 334, 200 (2011) Quantum phases of matter are characterized by the underlying correlations of
the many-body system. Although this is typically captured by a local order
parameter, it has been ...shown that a broad class of many-body systems possesses
a hidden non-local order. In the case of bosonic Mott insulators, the ground
state properties are governed by quantum fluctuations in the form of correlated
particle-hole pairs that lead to the emergence of a non-local string order in
one dimension. Using high-resolution imaging of low-dimensional quantum gases
in an optical lattice, we directly detect these pairs with single-site and
single-particle sensitivity and observe string order in the one-dimensional
case.
The expanding field of extracellular vesicle (EV) research needs reproducible and accurate methods to characterize single EVs. Nanoparticle Tracking Analysis (NTA) is commonly used to determine EV ...concentration and diameter. As the EV field is lacking methods to easily confirm and validate NTA data, questioning the reliability of measurements remains highly important. In this regard, a comparison addressing measurement quality between different NTA devices such as Malvern's NanoSight NS300 or Particle Metrix' ZetaView has not yet been conducted. To evaluate the accuracy and repeatability of size and concentration determinations of both devices, we employed comparative methods including transmission electron microscopy (TEM) and single particle interferometric reflectance imaging sensing (SP-IRIS) by ExoView. Multiple test measurements with nanospheres, liposomes and ultracentrifuged EVs from human serum and cell culture supernatant were performed. Additionally, serial dilutions and freeze-thaw cycle-dependent EV decrease were measured to determine the robustness of each system. Strikingly, NanoSight NS300 exhibited a 2.0-2.1-fold overestimation of polystyrene and silica nanosphere concentration. By measuring serial dilutions of EV samples, we demonstrated higher accuracy in concentration determination by ZetaView (% BIAS range: 2.7-8.5) in comparison with NanoSight NS300 (% BIAS range: 32.9-36.8). The concentration measurements by ZetaView were also more precise (% CV range: 0.0-4.7) than measurements by NanoSight NS300 (% CV range: 5.4-10.7). On the contrary, quantitative TEM imaging indicated more accurate EV sizing by NanoSight NS300 (% D
TEM
range: 79.5-134.3) compared to ZetaView (% D
TEM
range: 111.8-205.7), while being equally repeatable (NanoSight NS300% CV range: 0.8-6.7; ZetaView: 1.4-7.8). However, both devices failed to report a peak EV diameter below 60 nm compared to TEM and SP-IRIS. Taken together, NTA devices differ strongly in their hardware and software affecting measuring results. ZetaView provided a more accurate and repeatable depiction of EV concentration, whereas NanoSight NS300 supplied size measurements of higher resolution.
Euterpe oleraceae is a large palm tree indigenous to the Amazon River and its tributaries and estuaries in South America. Its fruit, known as acai, is of great economic value to native people. In ...this study, a standardized freeze-dried acai fruit pulp/skin powder was used for all analyses and tests. Among many findings, anthocyanins (ACNs), proanthocyanidins (PACs), and other flavonoids were found to be the major phytochemicals. Two ACNs, cyandin 3-glucoside and cyanidin 3-rutinoside were found to be predominant ACNs; three others were also found as minor ACNs. The total content of ACNs was measured as 3.1919 mg/g dry weight (DW). Polymers were found to be the major PACs. The concentration of total PACs was calculated as 12.89 mg/g DW. Other flavonoids, namely, homoorientin, orientin, isovitexin, scoparin, and taxifolin deoxyhexose, along with several unknown flavonoids, were also detected. Resveratrol was found but at a very low concentration. In addition, components including fatty acids, amino acids, sterols, minerals, and other nutrients were analyzed and quantified. Total polyunsaturated fatty acid, total monounsaturated fatty acid, and total saturated fatty acids contributed to 11.1%, 60.2%, and 28.7% of total fatty acid. Oleic acid (53.9%) and palmitic acid (26.7%) were found to be the two dominant fatty acids. Nineteen amino acids were found; the total amino acid content was determined to be 7.59% of total weight. The total sterols accounted for 0.048% by weight of powder. The three sterols B-sitosterol, campesterol, and sigmasterol were identified. A complete nutrient analysis is also presented. Microbiological analysis was also performed.
The m‐AAA protease subunit AFG3L2 is involved in degradation and processing of substrates in the inner mitochondrial membrane. Mutations in AFG3L2 are associated with spinocerebellar ataxia SCA28 in ...humans and impair axonal development and neuronal survival in mice. The loss of AFG3L2 causes fragmentation of the mitochondrial network. However, the pathogenic mechanism of neurodegeneration in the absence of AFG3L2 is still unclear. Here, we show that depletion of AFG3L2 leads to a specific defect of anterograde transport of mitochondria in murine cortical neurons. We observe similar transport deficiencies upon loss of AFG3L2 in OMA1‐deficient neurons, indicating that they are not caused by OMA1‐mediated degradation of the dynamin‐like GTPase OPA1 and inhibition of mitochondrial fusion. Treatment of neurons with antioxidants, such as N‐acetylcysteine or vitamin E, or decreasing tau levels in axons restored mitochondrial transport in AFG3L2‐depleted neurons. Consistently, tau hyperphosphorylation and activation of ERK kinases are detected in mouse neurons postnatally deleted for Afg3l2. We propose that reactive oxygen species signaling leads to cytoskeletal modifications that impair mitochondrial transport in neurons lacking AFG3L2.
Synopsis
Lack of the m‐AAA protease subunit AFG3L2 impairs anterograde axonal transport of mitochondria via a mechanism that involves ROS signaling and hyperphosphorylation of the microtubule‐associated protein tau.
Depletion of AFG3L2 in cortical neurons leads to a specific defect of anterograde axonal transport of mitochondria.
The mitochondrial transport defect is independent from OMA1‐dependent OPA1 processing.
Anterograde axonal transport of mitochondria in AFG3L2‐depleted neurons is rescued by reducing tau levels and by treatment with antioxidants.
Deletion of Afg3l2 in cortical neurons activates ERK kinases and leads to tau hyperphosphorylation.
Impaired axonal transport of mitochondria in the absence of AFG3L2 may explain how its mutation in spinocerebellar ataxia impair neuronal development and survival, and suggests possible therapeutic strategies based on counteracting ROS signaling.
The water hydration shell has a decisive impact on the structural and functional properties of RNA. Changes of the RNA structure upon melting and in biochemical processes are accompanied by a change ...of hydration patterns, a process that is barely characterized. To discern hydration geometries around the backbone phosphate groups of an RNA double helix at the molecular level, we combine two-dimensional infrared spectroscopy of phosphate vibrations with theoretical simulations. There are three distinct coexisting hydration motifs of the RNA A-helix: an ordered chain-like arrangement of water molecules with links between neighboring phosphate groups, separate local hydration shells of up to six water molecules, and hydrated phosphate/counterion contact pairs. RNA disordering upon melting is connected with a transition from predominantly ordered water structures to local hydration shells around phosphate units. Structural fluctuations are dominated by librational water motions occurring on a 300 fs time scale, without exchange between hydration motifs.
Ions interacting with hydrated RNA play a central role in defining its secondary and tertiary structure. While spatial arrangements of ions, water molecules, and phosphate groups have been inferred ...from X-ray studies, the role of electrostatic and other noncovalent interactions in stabilizing compact folded RNA structures is not fully understood at the molecular level. Here, we demonstrate that contact ion pairs of magnesium (Mg
) and phosphate groups embedded in local water shells stabilize the tertiary equilibrium structure of transfer RNA (tRNA). Employing dialyzed tRNA
from yeast and tRNA from
, we follow the population of Mg
sites close to phosphate groups of the ribose-phosphodiester backbone step by step, combining linear and nonlinear infrared spectroscopy of phosphate vibrations with molecular dynamics simulations and ab initio vibrational frequency calculations. The formation of up to six Mg
/phosphate contact pairs per tRNA and local field-induced reorientations of water molecules balance the phosphate-phosphate repulsion in nonhelical parts of tRNA, thus stabilizing the folded structure electrostatically. Such geometries display limited sub-picosecond fluctuations in the arrangement of water molecules and ion residence times longer than 1 μs. At higher Mg
excess, the number of contact ion pairs per tRNA saturates around 6 and weakly interacting ions prevail. Our results suggest a predominance of contact ion pairs over long-range coupling of the ion atmosphere and the biomolecule in defining and stabilizing the tertiary structure of tRNA.
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