13 research outputs found
The Neutron Star Mass Distribution
In recent years, the number of pulsars with secure mass measurements has
increased to a level that allows us to probe the underlying neutron star (NS)
mass distribution in detail. We critically review the radio pulsar mass
measurements. For the first time, we are able to analyze a sizable population
of NSs with a flexible modeling approach that can effectively accommodate a
skewed underlying distribution and asymmetric measurement errors. We find that
NSs that have evolved through different evolutionary paths reflect distinctive
signatures through dissimilar distribution peak and mass cutoff values. NSs in
double neutron star and neutron star-white dwarf systems show consistent
respective peaks at 1.33 Msun and 1.55 Msun suggesting significant mass
accretion (delta m~0.22 Msun) has occurred during the spin-up phase. The width
of the mass distribution implied by double NS systems is indicative of a tight
initial mass function while the inferred mass range is significantly wider for
NSs that have gone through recycling. We find a mass cutoff at ~2.1 Msun for
NSs with white dwarf companions which establishes a firm lower bound for the
maximum NS mass. This rules out the majority of strange quark and soft equation
of state models as viable configurations for NS matter. The lack of truncation
close to the maximum mass cutoff along with the skewed nature of the inferred
mass distribution both enforce the suggestion that the 2.1 Msun limit is set by
evolutionary constraints rather than nuclear physics or general relativity, and
the existence of rare super-massive NSs is possible.Comment: 13 pages, 4 figures, 2 tables. ApJ in press. A completely new and
more flexible statistical model applied. Astrophysical results remained same
as arXiv:1011.429
Oriented Assembly of Lead Halide Perovskite Nanocrystals
Cesium lead halide nanostructures have highly tunable
optical and
optoelectronic properties. Establishing precise control in forming
perovskite single-crystal nanostructures is key to unlocking the full
potential of these materials. However, studying the growth kinetics
of colloidal cesium lead halides is challenging due to their sensitivity
to light, electron beam, and environmental factors like humidity.
In this study, in situ observations of CsPbBr3âparticle
dynamics were made possible through extremely low dose liquid cell
transmission electron microscopy, showing that oriented attachment
is the dominant pathway for the growth of single-crystal CsPbBr3 architectures from primary nanocubes. In addition, oriented
assembly and fusion of ligand-stabilized cubic CsPbBr3 nanocrystals
are promoted by electron beam irradiation or introduction of polar
additives that both induce partial desorption of the original ligands
and polarize the nanocube surfaces. These findings advance our understanding
of cesium lead halide growth mechanisms, aiding the controlled synthesis
of other perovskite nanostructures
Oriented Assembly of Lead Halide Perovskite Nanocrystals
Cesium lead halide nanostructures have highly tunable
optical and
optoelectronic properties. Establishing precise control in forming
perovskite single-crystal nanostructures is key to unlocking the full
potential of these materials. However, studying the growth kinetics
of colloidal cesium lead halides is challenging due to their sensitivity
to light, electron beam, and environmental factors like humidity.
In this study, in situ observations of CsPbBr3âparticle
dynamics were made possible through extremely low dose liquid cell
transmission electron microscopy, showing that oriented attachment
is the dominant pathway for the growth of single-crystal CsPbBr3 architectures from primary nanocubes. In addition, oriented
assembly and fusion of ligand-stabilized cubic CsPbBr3 nanocrystals
are promoted by electron beam irradiation or introduction of polar
additives that both induce partial desorption of the original ligands
and polarize the nanocube surfaces. These findings advance our understanding
of cesium lead halide growth mechanisms, aiding the controlled synthesis
of other perovskite nanostructures
Oriented Assembly of Lead Halide Perovskite Nanocrystals
Cesium lead halide nanostructures have highly tunable
optical and
optoelectronic properties. Establishing precise control in forming
perovskite single-crystal nanostructures is key to unlocking the full
potential of these materials. However, studying the growth kinetics
of colloidal cesium lead halides is challenging due to their sensitivity
to light, electron beam, and environmental factors like humidity.
In this study, in situ observations of CsPbBr3âparticle
dynamics were made possible through extremely low dose liquid cell
transmission electron microscopy, showing that oriented attachment
is the dominant pathway for the growth of single-crystal CsPbBr3 architectures from primary nanocubes. In addition, oriented
assembly and fusion of ligand-stabilized cubic CsPbBr3 nanocrystals
are promoted by electron beam irradiation or introduction of polar
additives that both induce partial desorption of the original ligands
and polarize the nanocube surfaces. These findings advance our understanding
of cesium lead halide growth mechanisms, aiding the controlled synthesis
of other perovskite nanostructures
Atomic Force Microscopy-Based Force Spectroscopy and Multiparametric Imaging of Biomolecular and Cellular Systems
During the last three decades, a series of key technological improvements turned atomic force microscopy (AFM) into a nanoscopic laboratory to directly observe and chemically characterize molecular and cell biological systems under physiological conditions. Here, we review key technological improvements that have established AFM as an analytical tool to observe and quantify native biological systems from the micro- to the nanoscale. Native biological systems include living tissues, cells, and cellular components such as single or complexed proteins, nucleic acids, lipids, or sugars. We showcase the procedures to customize nanoscopic chemical laboratories by functionalizing AFM tips and outline the advantages and limitations in applying different AFM modes to chemically image, sense, and manipulate biosystems at (sub)nanometer spatial and millisecond temporal resolution. We further discuss theoretical approaches to extract the kinetic and thermodynamic parameters of specific biomolecular interactions detected by AFM for single bonds and extend the discussion to multiple bonds. Finally, we highlight the potential of combining AFM with optical microscopy and spectroscopy to address the full complexity of biological systems and to tackle fundamental challenges in life sciences
SelfâAssembly and Oriented Growth of Conductive NiâCATâ1 MetalâOrganic Framework at SolidâLiquid Interfaces
Abstract Twoâdimensional (2D) conductive metalâorganic frameworks (MOF) represent a unique class of electrode materials with high capacity and power density. Understanding molecular mechanisms and pathways for heterogeneous nucleation of 2D Ïâconjugated MOFs is highly desirable for controlling the structure and properties of conductive MOFs on solid substrates. Herein, a systematic study of nucleation and growth of 2D Ïâconjugated Niâcatecholate (NiâCATâ1) MOFs on highly oriented pyrolytic graphite (HOPG) and copper substrates is reported. It is discovered that the nucleation density and growth kinetics of the MOF film can be controlled by varying substrate interactions with the organic linker. Specifically, ÏâÏ interactions between the linker and the HOPG dictate lower nucleation density, whereas Ïâmetal interactions between the linker and the copper substrate dictate faster nucleation and higher nucleation densities. These studies reveal the key mechanism for NiâCATâ1 nucleation on different surfaces and provide insights into interfacial control over the growth of other 2D Ïâconjugated MOF films on solid substrates to inform synthesis of functional materials
Double Epitaxy as a Paradigm for Templated Growth of Highly Ordered Three-Dimensional Mesophase Crystals
Molecular templating and self-assembly
are fundamental mechanisms
for controlling the morphology of biominerals, while in synthetic
two-dimensional layered materials similar levels of control over materials
structure can be achieved through the epitaxial relationship with
the substrate. In this study these two concepts are combined to provide
an approach for the nucleation and growth of three-dimensional ordered
mesophases on solid surfaces. A combined experimental and theoretical
study revealed how atomic ordering of the substrate controls the structure
of surfactant template and the orientation and morphology of the epitaxially
grown inorganic material. This dual epitaxial relationship between
the substrate, surfactant template, and inorganic mesophase gives
rise to a highly ordered porous mesophase with a well-defined cubic
lattice of pores. The level of control over the materialâs
three-dimensional architecture achieved in this one-step synthesis
is reminiscent of that in biomineralization