777 research outputs found
Ultracold atoms in optical lattices
Bosonic atoms trapped in an optical lattice at very low temperatures, can be
modeled by the Bose-Hubbard model. In this paper, we propose a slave-boson
approach for dealing with the Bose-Hubbard model, which enables us to
analytically describe the physics of this model at nonzero temperatures. With
our approach the phase diagram for this model at nonzero temperatures can be
quantified.Comment: 29 pages, 10 figure
Modelling and experiments of self-reflectivity under femtosecond ablation conditions
We present a numerical model which describes the propagation of a single
femtosecond laser pulse in a medium of which the optical properties dynamically
change within the duration of the pulse. We use a Finite Difference Time Domain
(FDTD) method to solve the Maxwell's equations coupled to equations describing
the changes in the material properties. We use the model to simulate the
self-reflectivity of strongly focused femtosecond laser pulses on silicon and
gold under laser ablation condition. We compare the simulations to experimental
results and find excellent agreement.Comment: 11 pages, 8 figure
Mott insulators in an optical lattice with high filling factors
We discuss the superfluid to Mott insulator transition of an atomic Bose gas
in an optical lattice with high filling factors. We show that also in this
multi-band situation, the long-wavelength physics is described by a single-band
Bose-Hubbard model. We determine the many-body renormalization of the tunneling
and interaction parameters in the effective Bose-Hubbard Hamiltonian, and
consider the resulting model at nonzero temperatures. We show that in
particular for a one or two-dimensional optical lattice, the Mott insulator
phase is more difficult to realize than anticipated previously.Comment: 5 pages, 3 figures, title changed, major restructuring, resubmitted
to PR
Mean-field theory for Bose-Hubbard Model under a magnetic field
We consider the superfluid-insulator transition for cold bosons under an
effective magnetic field. We investigate how the applied magnetic field affects
the Mott transition within mean field theory and find that the critical hopping
strength , increases with the applied field. The increase in the
critical hopping follows the bandwidth of the Hofstadter butterfly at the given
value of the magnetic field. We also calculate the magnetization and superfluid
density within mean field theory.Comment: 11 pages, 7 figures, published versio
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Nitrogen cycle dynamics during the Cretaceous Oceanic Anoxic Event 2 (OAE2; ~94 Ma) in the Western Interior Seaway
The Cretaceous Ocean Anoxic Event 2 (OAE2, ~94 Ma), a time period of high sea-level and a warm greenhouse climate, was characterized by enhanced marine productivity and carbon burial in sediments, which resulted in the widespread deposition of black shales and a global perturbation of the carbon cycle. While decades of research have disentangled complex ecological dynamics during OAE2, a detailed understanding of the nitrogen cycle during this event (i.e., nitrogen transformations through metabolic and/or water-column redox reactions), remains elusive. I present a high-resolution (~300-3,000 years) bulk organic nitrogen stable isotope record from an expanded sedimentary section of OAE2 in the Smokey Hollow #1 core (SH1, southern Utah) that provides a record of changes in marine biogeochemistry from a marginal setting in the Western Interior Seaway (WIS). The δ13Corg record shows the characteristic chemostratigraphic phases of OAE2 seen globally. The δ15Norg record shows a 2-phased 15N depletion of ~6‰, which is a larger than has been previously reported during OAE2, and may suggest a buildup of 15N depleted ammonium from efficient nitrogen remineralization. Variations in the C/N ratio from 1.8 to 30.2 reflect variable input of organic matter sources to the study area throughout the event, including terrestrial (soil) and marine organic matter. The δ15Norg record exhibits a moderate but statistically significant correlation with available data on terrestrial-derived biomarkers, likely reflecting the impact of transgressional sequences and/or terrestrial input on nitrogen cycle dynamics at this study location. My results indicate that nitrogen cycling in the western margin of the WIS was affected by increased recycling of ammonium in the oceans, as well as changes in nitrogen input from continental sources, across OAE2.</p
Selecting Potential Targetable Biomarkers for Imaging Purposes in Colorectal Cancer Using TArget Selection Criteria (TASC):A Novel Target Identification Tool
Peritoneal carcinomatosis (PC) of colorectal origin is associated with a poor prognosis. However, cytoreductive surgery combined with hyperthermic intraperitoneal chemotherapy is available for a selected group of PC patients, which significantly increases overall survival rates up to 30%. As a consequence, there is substantial room for improvement. Tumor targeting is expected to improve the treatment efficacy of colorectal cancer (CRC) further through 1) more sensitive preoperative tumor detection, thus reducing overtreatment; 2) better intraoperative detection and surgical elimination of residual disease using tumor-specific intraoperative imaging; and 3) tumor-specific targeted therapeutics. This review focuses, in particular, on the development of tumor-targeted imaging agents. A large number of biomarkers are known to be upregulated in CRC. However, to date, no validated criteria have been described for the selection of the most promising biomarkers for tumor targeting. Such a scoring system might improve the selection of the correct biomarker for imaging purposes. In this review, we present the TArget Selection Criteria (TASC) scoring system for selection of potential biomarkers for tumor-targeted imaging. By applying TASC to biomarkers for CRC, we identified seven biomarkers (carcinoembryonic antigen, CXC chemokine receptor 4, epidermal growth factor receptor, epithelial cell adhesion molecule, matrix metalloproteinases, mucin 1, and vascular endothelial growth factor A) that seem most suitable for tumor-targeted imaging applications in colorectal cancer. Further cross-validation studies in CRC and other tumor types are necessary to establish its definitive value
Cross-talk between signaling pathways leading to defense against pathogens and insects
In nature, plants interact with a wide range of organisms, some of which
are harmful (e.g. pathogens, herbivorous insects), while others are beneficial
(e.g. growth-promoting rhizobacteria, mycorrhizal fungi, and predatory
enemies of herbivores). During the evolutionary arms race between plants
and their attackers, primary and secondary immune responses evolved to
recognize common or highly specialized features of microbial pathogens
(Chisholm et al., 2006), resulting in sophisticated mechanisms of defense
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