4,374 research outputs found
Division, adjoints, and dualities of bilinear maps
The distributive property can be studied through bilinear maps and various
morphisms between these maps. The adjoint-morphisms between bilinear maps
establish a complete abelian category with projectives and admits a duality.
Thus the adjoint category is not a module category but nevertheless it is
suitably familiar. The universal properties have geometric perspectives. For
example, products are orthogonal sums. The bilinear division maps are the
simple bimaps with respect to nondegenerate adjoint-morphisms. That formalizes
the understanding that the atoms of linear geometries are algebraic objects
with no zero-divisors. Adjoint-isomorphism coincides with principal isotopism;
hence, nonassociative division rings can be studied within this framework.
This also corrects an error in an earlier pre-print; see Remark 2.11
Curve classes on irreducible holomorphic symplectic varieties
We prove that the integral Hodge conjecture holds for 1-cycles on irreducible
holomorphic symplectic varieties of K3 type and of Generalized Kummer type. As
an application, we give a new proof of the integral Hodge conjecture for cubic
fourfolds.Comment: 15 page
Coherent strong-field control of multiple states by a single chirped femtosecond laser pulse
We present a joint experimental and theoretical study on strong-field
photo-ionization of sodium atoms using chirped femtosecond laser pulses. By
tuning the chirp parameter, selectivity among the population in the highly
excited states 5p, 6p, 7p and 5f, 6f is achieved. Different excitation pathways
enabling control are identified by simultaneous ionization and measurement of
photoelectron angular distributions employing the velocity map imaging
technique. Free electron wave packets at an energy of around 1 eV are observed.
These photoelectrons originate from two channels. The predominant 2+1+1
Resonance Enhanced Multi-Photon Ionization (REMPI) proceeds via the strongly
driven two-photon transition , and subsequent
ionization from the states 5p, 6p and 7p whereas the second pathway involves
3+1 REMPI via the states 5f and 6f. In addition, electron wave packets from
two-photon ionization of the non-resonant transiently populated state 3p are
observed close to the ionization threshold. A mainly qualitative five-state
model for the predominant excitation channel is studied theoretically to
provide insights into the physical mechanisms at play. Our analysis shows that
by tuning the chirp parameter the dynamics is effectively controlled by dynamic
Stark-shifts and level crossings. In particular, we show that under the
experimental conditions the passage through an uncommon three-state "bow-tie"
level crossing allows the preparation of coherent superposition states
Complete genome sequences of two phylogenetically distinct Nitrospina strains isolated from the Atlantic and Pacific Oceans
This paper is not subject to U.S. copyright. The definitive version was published in Bayer, B., Kellom, M., Valois, F., Waterbury, J., & Santoro, A. Complete genome sequences of two phylogenetically distinct Nitrospina strains isolated from the Atlantic and Pacific Oceans. Microbiology Resource Announcements, 11(5), (2022): e00100–e00122, https://doi.org/10.1128/mra.00100-22.The complete genome sequences of two chemoautotrophic nitrite-oxidizing bacteria of the genus Nitrospina are reported. Nitrospina gracilis strain Nb-211 was isolated from the Atlantic Ocean, and Nitrospina sp. strain Nb-3 was isolated from the Pacific Ocean. We report two highly similar ~3.07-Mbp genome sequences that differ by the presence of ferric iron chelator (siderophore) biosynthesis genes.This work was supported by a Simons Foundation Early Career Investigator Award (3435889) and a U.S. National Science Foundation award OCE-1924512 to A.E.S. B.B. was supported by the Austrian Science Fund (FWF) project number J4426-B. The work conducted by the U.S. Department of Energy Joint Genome Institute, a DOE Office of Science User Facility, is supported under contract number DE-AC02-05CH11231. These data were generated for JGI proposal number 506203 to B.B. and A.E.S
Optical measurements of spin noise as a high resolution spectroscopic tool
The intrinsic fluctuations of electron spins in semiconductors and atomic
vapors generate a small, randomly-varying "spin noise" that can be detected by
sensitive optical methods such as Faraday rotation. Recent studies have
demonstrated that the frequency, linewidth, and lineshape of this spin noise
directly reveals dynamical spin properties such as dephasing times, relaxation
mechanisms and g-factors without perturbing the spins away from equilibrium.
Here we demonstrate that spin noise measurements using wavelength-tunable probe
light forms the basis of a powerful and novel spectroscopic tool to provide
unique information that is fundamentally inaccessible via conventional linear
optics. In particular, the wavelength dependence of the detected spin noise
power can reveal homogeneous linewidths buried within inhomogeneously-broadened
optical spectra, and can resolve overlapping optical transitions belonging to
different spin systems. These new possibilities are explored both theoretically
and via experiments on spin systems in opposite limits of inhomogeneous
broadening (alkali atom vapors and semiconductor quantum dots).Comment: 4 pages, 4 figure
Effect of pump-probe detuning on the Faraday rotation and ellipticity signals of mode-locked spins in InGaAs quantum dots
We have studied the Faraday rotation and ellipticity signals in ensembles of
singly-charged (In,Ga)As/GaAs quantum dots by pump-probe spectroscopy. For
degenerate pump and probe we observe that the Faraday rotation signal amplitude
first grows with increasing the time separation between pump and probe before a
decay is observed for large temporal separations. The temporal behavior of the
ellipticity signal, on the other hand, is regular: its amplitude decays with
the separation. By contrast, for detuned pump and probe the Faraday rotation
and ellipticty signals both exhibit similar and conventional behavior. The
experimental results are well described in the frame of a recently developed
microscopic theory [Phys. Rev. B 80, 104436 (2009)]. The comparison between
calculations and experimental data allows us to provide insight into the
spectral dependence of the electron spin precession frequencies and extract the
electron g-factor dependence on energy.Comment: 9 pages, 7 figure
Control of interlayer exchange coupling in Fe/Cr/Fe trilayers by ion beam irradiation
The manipulation of the antiferromagnetic interlayer coupling in the
epitaxial Fe/Cr/Fe(001) trilayer system by moderate 5 keV He ion beam
irradiation has been investigated experimentally. It is shown that even for
irradiation with very low fluences (10^14 ions/cm^2) a drastic change in
strength of the coupling appears. For thin Cr-spacers (below 0.6 - 0.7 nm) the
coupling strength decreases with fluence, becoming ferromagnetic for fluences
above (2x10^14 ions/cm^2). The effect is connected with the creation of
magnetic bridges in the layered system due to atomic exchange events caused by
the bombardment. For thicker Cr spacers (0.8 - 1.2 nm) an enhancement of the
antiferromagnetic coupling strength is found. A possible explanation of the
enhancement effect is given.Comment: Submitted to PR
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