191 research outputs found
One-dimensional surface states on a striped Ag thin film with stacking fault arrays
One-dimensional (1D) stripe structures with a periodicity of 1.3 nm are
formed by introduction of stacking fault arrays into a Ag thin film. The
surface states of such striped Ag thin films are studied using a low
temperature scanning tunneling microscope. Standing waves running in the
longitudinal direction and characteristic spectral peaks are observed by
differential conductance (dI/dV) measurements, revealing the presence of 1D
states on the surface stripes. Their formation can be attributed to quantum
confinement of Ag(111) surface states into a stripe by stacking faults. To
quantify the degree of confinement, the effective potential barrier at the
stacking fault for Ag(111) surface states is estimated from independent
measurements. A single quantum well model with the effective potential barrier
can reproduce the main features of dI/dV spectra on stripes, while a
Kronig-Penney model fails to do so. Thus the present system should be viewed as
decoupled 1D states on individual stripes rather than as anisotropic 2D Bloch
states extending over a stripe array.Comment: 10 pages, 6 figure
Influence of age, reproductive cycling status, and menstruation on the vaginal microbiome in baboons (Papio anubis)
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111197/1/ajp22378.pd
Carbon fibre tips for scanning probe microscopy based on quartz tuning fork force sensors
We report the fabrication and the characterization of carbon fibre tips for
their use in combined scanning tunnelling and force microscopy based on
piezoelectric quartz tuning fork force sensors. We find that the use of carbon
fibre tips results in a minimum impact on the dynamics of quartz tuning fork
force sensors yielding a high quality factor and consequently a high force
gradient sensitivity. This high force sensitivity in combination with high
electrical conductivity and oxidation resistance of carbon fibre tips make them
very convenient for combined and simultaneous scanning tunnelling microscopy
and atomic force microscopy measurements. Interestingly, these tips are quite
robust against occasionally occurring tip crashes. An electrochemical
fabrication procedure to etch the tips is presented that produces a sub-100 nm
apex radius in a reproducible way which can yield high resolution images.Comment: 14 pages, 10 figure
Macroscopic Superconducting Current through a Silicon Surface Reconstruction with Indium Adatoms: Si(111)-(R7R3)-In
Macroscopic and robust supercurrents are observed by direct electron
transport measurements on a silicon surface reconstruction with In adatoms
(Si(111)-(R7xR3)-In). The superconducting transition manifests itself as an
emergence of the zero resistance state below 2.8 K. characteristics
exhibit sharp and hysteretic switching between superconducting and normal
states with well-defined critical and retrapping currents. The two-dimensional
(2D) critical current density is estimated to be as high as
at 1.8 K. The temperature dependence of
indicates that the surface atomic steps play the role of strongly coupled
Josephson junctions.Comment: 4 pages, 3 figures; The error in the values of 2D critical current
density was corrected. In the old version, the numbers were
wrong by a factor of 100 due to a mechanical error. This does not affect the
following analysis and conclusio
Structural basis of nucleosome assembly by the Abo1 AAA+ ATPase histone chaperone
The fundamental unit of chromatin, the nucleosome, is an intricate structure that requires histone chaperones for assembly. ATAD2 AAA+???ATPases are a family of histone chaperones that regulate nucleosome density and chromatin dynamics. Here, we demonstrate that the fission yeast ATAD2 homolog, Abo1, deposits histone H3???H4 onto DNA in an ATP-hydrolysis-dependent manner by in vitro reconstitution and single-tethered DNA curtain assays. We present cryo-EM structures of an ATAD2 family ATPase to atomic resolution in three different nucleotide states, revealing unique structural features required for histone loading on DNA, and directly visualize the transitions of Abo1 from an asymmetric spiral (ATP-state) to a symmetric ring (ADP- and apo-states) using high-speed atomic force microscopy (HS-AFM). Furthermore, we find that the acidic pore of ATP-Abo1 binds a peptide substrate which is suggestive of a histone tail. Based on these results, we propose a model whereby Abo1 facilitates H3???H4 loading by utilizing ATP
High-speed AFM height spectroscopy reveals µs-dynamics of unlabeled biomolecules
Dynamics are fundamental to the functions of biomolecules and can occur on a wide range of time and length scales. Here we develop and apply high-speed AFM height spectroscopy (HS-AFM-HS), a technique whereby we monitor the sensing of a HS-AFM tip at a fixed position to directly detect the motions of unlabeled molecules underneath. This gives Angstrom spatial and microsecond temporal resolutions. In conjunction with HS-AFM imaging modes to precisely locate areas of interest, HS-AFM-HS measures simultaneously surface concentrations, diffusion coefficients and oligomer sizes of annexin-V on model membranes to decipher key kinetics allowing us to describe the entire annexin-V membrane-association and self-assembly process in great detail and quantitatively. This work displays how HS-AFM-HS can assess the dynamics of unlabeled bio-molecules over several orders of magnitude and separate the various dynamic components spatiotemporally
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