12,006 research outputs found
A 0.18ÎŒm CMOS 300MHz Current-Mode LF Seventh-order Linear Phase Filter for Hard Disk Read Channels
âThis material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder." âCopyright IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.âA 300MHz CMOS seventh-order linear phase gm-C filter based on a current-mode multiple loop feedback (MLF) leap-frog (LF) structure is realized. The filter is implemented using a fully-differential linear operational transconductance amplifier (OTA) based on a source degeneration topology. PSpice simulations using a standard TSMC 0.18ÎŒm CMOS process with 2.5V power supply have shown that the cut-off frequency of the filter can be tuned from 260MHz to 320MHz and dynamic range is about 66dB. Group delay ripple is approximately 4.5% over the whole tuning range and maximum power consumption is 210mW
A 0.18ÎŒm CMOS 9mW current-mode FLF linear phase filter with gain boost
âThis material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder." âCopyright IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.âThe design and implementation of a CMOS continuous-time follow-the-leader-feedback (FLF) filter is described. The filter is implemented using a fully-differential linear, low voltage and low power consumption operational transconductance amplifier (OTA) based on a source degeneration topology. PSpice simulations using a standard TSMC 0.18 mum CMOS process with 2 V power supply have shown that the cut-off frequency of the filter ranges from 55 MHz to 160 MHz and dynamic range is about 45 dB. The group delay is less than 5% over the whole tuning range; the power consumption is only 9 mW
Time-resolved photoemission of correlated electrons driven out of equilibrium
We describe the temporal evolution of the time-resolved photoemission
response of the spinless Falicov-Kimball model driven out of equilibrium by
strong applied fields. The model is one of the few possessing a metal-insulator
transition and admitting an exact solution in the time domain. The
nonequilibrium dynamics, evaluated using an extension of dynamical mean-field
theory, show how the driven system differs from two common viewpoints - a
quasiequilibrium system at an elevated effective temperature (the "hot"
electron model) or a rapid interaction quench ("melting" of the Mott gap) - due
to the rearrangement of electronic states and redistribution of spectral
weight. The results demonstrate the inherent trade-off between energy and time
resolution accompanying the finite width probe pulses, characteristic of those
employed in pump-probe time-domain experiments, which can be used to focus
attention on different aspects of the dynamics near the transition.Comment: Original: 5 pages, 3 figures; Replaced: updated text and figures, 5
pages, 4 figure
Interpretation of X-ray Absorption Spectroscopy in the Presence of Surface Hybridization
X-ray absorption spectroscopy yields direct access to the electronic and
geometric structure of hybrid inorganic-organic interfaces formed upon
adsorption of complex molecules at metal surfaces. The unambiguous
interpretation of corresponding spectra is challenged by the intrinsic
geometric flexibility of the adsorbates and the chemical interactions with the
interface. Density-functional theory (DFT) calculations of the extended
adsorbate-substrate system are an established tool to guide peak assignment in
X-ray photoelectron spectroscopy (XPS) of complex interfaces. We extend this to
the simulation and interpretation of X-ray absorption spectroscopy (XAS) data
in the context of functional organic molecules on metal surfaces using
dispersion-corrected DFT calculations within the transition potential approach.
On the example of X-ray absorption signatures for the prototypical case of
2H-porphine adsorbed on Ag(111) and Cu(111) substrates, we follow the two main
effects of the molecule/surface interaction on XAS: (1) the substrate-induced
chemical shift of the 1s core levels that dominates in physisorbed systems and
(2) the hybridization-induced broadening and loss of distinct resonances that
dominates in more chemisorbed systems.Comment: 13 pages, 4 figure
Dynamic Freeze-In: Impact of Thermal Masses and Cosmological Phase Transitions on Dark Matter Production
The cosmological abundance of dark matter can be significantly influenced by
the temperature dependence of particle masses and vacuum expectation values. We
illustrate this point in three simple freeze-in models. The first one, which we
call kinematically induced freeze-in, is based on the observation that the
effective mass of a scalar temporarily becomes very small as the scalar
potential undergoes a second order phase transition. This opens dark matter
production channels that are otherwise forbidden. The second model we consider,
dubbed vev-induced freeze-in, is a fermionic Higgs portal scenario. Its scalar
sector is augmented compared to the Standard Model by an additional scalar
singlet, , which couples to dark matter and temporarily acquires a vacuum
expectation value (a two-step phase transition or `vev flip-flop'). While
, the modified coupling structure in the scalar
sector implies that dark matter production is significantly enhanced compared
to the phases realised at very early times and again
today. The third model, which we call mixing-induced freeze-in, is similar in
spirit, but here it is the mixing of dark sector fermions, induced by non-zero
, that temporarily boosts the dark matter production rate.
For all three scenarios, we carefully dissect the evolution of the dark sector
in the early Universe. We compute the DM relic abundance as a function of the
model parameters, emphasising the importance of thermal corrections and the
proper treatment of phase transitions in the calculation.Comment: 26 pages, 11 figures, v2: matches journal version, change to the
value of a benchmark coupling in section II, impact of thermal masses
increase
Functional hybrid rubisco enzymes with plant small subunits and algal large subunits: engineered rbcS cDNA for expression in chlamydomonas.
There has been much interest in the chloroplast-encoded large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) as a target for engineering an increase in net CO(2) fixation in photosynthesis. Improvements in the enzyme would lead to an increase in the production of food, fiber, and renewable energy. Although the large subunit contains the active site, a family of rbcS nuclear genes encodes the Rubisco small subunits, which can also influence the carboxylation catalytic efficiency and CO(2)/O(2) specificity of the enzyme. To further define the role of the small subunit in Rubisco function, small subunits from spinach, Arabidopsis, and sunflower were assembled with algal large subunits by transformation of a Chlamydomonas reinhardtii mutant that lacks the rbcS gene family. Foreign rbcS cDNAs were successfully expressed in Chlamydomonas by fusing them to a Chlamydomonas rbcS transit peptide sequence engineered to contain rbcS introns. Although plant Rubisco generally has greater CO(2)/O(2) specificity but a lower carboxylation V(max) than Chlamydomonas Rubisco, the hybrid enzymes have 3-11% increases in CO(2)/O(2) specificity and retain near normal V(max) values. Thus, small subunits may make a significant contribution to the overall catalytic performance of Rubisco. Despite having normal amounts of catalytically proficient Rubisco, the hybrid mutant strains display reduced levels of photosynthetic growth and lack chloroplast pyrenoids. It appears that small subunits contain the structural elements responsible for targeting Rubisco to the algal pyrenoid, which is the site where CO(2) is concentrated for optimal photosynthesis.This work was supported in part by Grant DE-FG02-00ER15044 from the United States Department of Energy
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