2,166 research outputs found
Flexural pivots for space applications
Design and fabrication of flexible pivots for aerospace structure
Post-resolution treatment of depositors at failed banks: implications for the severity of banking crises, systemic risk, and too-big-to-fail
Bank failures are widely viewed in all countries as more damaging to the economy than the failure of other firms of similar size for a number of reasons. The failures may produce losses to depositors and other creditors, break long-standing bank-customers loan relationships, disrupt the payments system, and spillover in domino fashion to other banks, financial institutions and markets, and even to the macroeconomy (Kaufman, 1996). Thus, bank failures are viewed as potentially more likely to involve contagion or systemic risk than the collapse of other firms. The risk of such actual or perceived damage is often a popular justification for explicit or implicit government-provided or sponsored safety nets under banks, including explicit deposit insurance and implicit government guarantees, such as "too-big-to-fail" (TBTF), that may protect de jure uninsured depositors and possibly other bank stakeholders against some or all of the loss.Bank failures ; Deposit insurance
Axial motion estimation and correction for simultaneous multi-plane two-photon calcium imaging
Two-photon imaging in behaving animals is typically accompanied by brain motion. For functional imaging experiments, for example with genetically encoded calcium indicators, such brain motion induces changes in fluorescence intensity. These motion-related intensity changes or motion artifacts can typically not be separated from neural activity-induced signals. While lateral motion, within the focal plane, can be corrected by computationally aligning images, axial motion, out of the focal plane, cannot easily be corrected. Here, we developed an algorithm for axial motion correction for non-ratiometric calcium indicators taking advantage of simultaneous multi-plane imaging. Using temporally multiplexed beams, recording simultaneously from at least two focal planes at different z positions, and recording a z-stack for each beam as a calibration step, the algorithm separates motion-related and neural activity-induced changes in fluorescence intensity. The algorithm is based on a maximum likelihood optimisation approach; it assumes (as a first order approximation) that no distortions of the sample occurs during axial motion and that neural activity increases uniformly along the optical axis in each region of interest. The developed motion correction approach allows axial motion estimation and correction at high frame rates for isolated structures in the imaging volume in vivo, such as sparse expression patterns in the fruit fly brain
Axial motion estimation and correction for simultaneous multi-plane two-photon calcium imaging
Two-photon imaging in behaving animals is typically accompanied by brain motion. For functional imaging experiments, for example with genetically encoded calcium indicators, such brain motion induces changes in fluorescence intensity. These motion related intensity changes or motion artifacts cannot easily be separated from neural activity induced signals. While lateral motion within the focal plane can be corrected by computationally aligning images, axial motion, out of the focal plane, cannot easily be corrected. Here, we develop an algorithm for axial motion correction for non-ratiometric calcium indicators taking advantage of simultaneous multi-plane imaging. Using at least two simultaneously recorded focal planes, the algorithm separates motion related and neural activity induced changes in fluorescence intensity. The developed motion correction approach allows axial motion estimation and correction at high frame rates for isolated structures in the imaging volume in vivo, such as sparse expression patterns in the fruit fly brain
Pancreatic Resections for Advanced M1-Pancreatic Carcinoma: The Value of Synchronous Metastasectomy
Background. For M1 pancreatic adenocarcinomas pancreatic resection is usually not indicated. However, in highly selected patients synchronous metastasectomy may be appropriate together with pancreatic resection when operative morbidity is low.
Materials and Methods. From January 1, 2004 to December, 2007 a total of 20 patients with pancreatic malignancies were retrospectively evaluated who underwent pancreatic surgery with synchronous resection of hepatic, adjacent organ, or peritoneal metastases for proven UICC stage IV periampullary cancer of the pancreas. Perioperative as well as clinicopathological parameters were evaluated.
Results. There were 20 patients (9 men, 11 women; mean age 58 years) identified. The primary tumor was located in the pancreatic head (n = 9, 45%), in pancreatic tail (n = 9, 45%), and in the papilla Vateri (n = 2, 10%). Metastases were located in the liver (n = 14, 70%), peritoneum (n = 5, 25%), and omentum majus (n = 2, 10%). Lymphnode metastases were present in 16 patients (80%). All patients received resection of their tumors together with metastasectomy. Pylorus preserving duodenopancreatectomy was performed in 8 patients, distal pancreatectomy in 8, duodenopancreatectomy in 2, and total pancreatectomy in 2. Morbidity was 45% and there was no perioperative mortality. Median postoperative survival was 10.7 months (2.6–37.7 months) which was not significantly different from a matched-pair group of patients who underwent pancreatic resection for UICC adenocarcinoma of the pancreas (median survival 15.6 months; P = .1). Conclusion. Pancreatic resection for M1 periampullary cancer of the pancreas can be performed safely in well-selected patients. However, indication for surgery has to be made on an individual basis
Automated long-term two-photon imaging in head-fixed walking Drosophila
The brain of Drosophila shows dynamics at multiple timescales, from the millisecond range of fast voltage or calcium transients to functional and structural changes occurring over multiple days. To relate such dynamics to behavior requires monitoring neural circuits across these multiple timescales in behaving animals. Here, we develop a technique for automated long-term two-photon imaging in fruit flies, during wakefulness and sleep, navigating in virtual reality over up to seven days. The method is enabled by laser surgery, a microrobotic arm for controlling forceps for dissection assistance, an automated feeding robot, as well as volumetric, simultaneous multiplane imaging. The approach is validated in the fly’s head direction system. Imaging in behaving flies over multiple timescales will be useful for understanding circadian activity, learning and long-term memory, or sleep
Research Article
[Abstract] During sleep, the brain undergoes dynamic and structural changes. In Drosophila, such changes have been observed in the central complex, a brain area important for sleep control and navigation. The connectivity of the central complex raises the question about how navigation, and specifically the head direction system, can operate in the face of sleep related plasticity. To address this question, we develop a model that integrates sleep homeostasis and head direction. We show that by introducing plasticity, the head direction system can function in a stable way by balancing plasticity in connected circuits that encode sleep pressure. With increasing sleep pressure, the head direction system nevertheless becomes unstable and a sleep phase with a different plasticity mechanism is introduced to reset network connectivity. The proposed integration of sleep homeostasis and head direction circuits captures features of their neural dynamics observed in flies and mice.[Author summary] In Drosophila, sleep and navigation are largely disconnected fields, even though the same brain structures and connected neural circuits are important for the two different functionalities. Motivated by experimental results from both fields as well as the connectome, we use theoretical modeling to describe the coupled dynamics of homeostatic sleep and navigation circuits in the central complex of Drosophila. The resulting model can incorporate and explain several experimental findings about sleep and navigation in flies and mice. The model is based on a ring attractor network which is combined with plasticity rules that change between sleep and wake phases and shows autonomous dynamics during sleep, reminiscent of observations in the head direction system of mice
Integration of sleep homeostasis and navigation in Drosophila
During sleep, the brain undergoes dynamic and structural changes. In Drosophila, such changes have been observed in the central complex, a brain area important for sleep control and navigation. For navigation, the structure and function of the central complex suggest a relationship to ring attractors, networks that model head direction. This raises the question about a similar structure-function relationship for sleep control.Motivated by experimental findings, we develop a ring attractor model that maintains activity at a setpoint in the face of plasticity. In this model, an integrator of sleep drive emerges with a functional role in stabilizing the network. Nevertheless, the network becomes unstable over extended wake time. Therefore, a sleep phase is introduced where autonomous attractor dynamics, related to its activity during wakefulness, reset the network. The proposed integration of sleep and head direction circuits captures features of their neural dynamics observed in flies and mice during wakefulness and sleep.Author Summary In Drosophila, the study of sleep and the study of navigation are largely disconnected fields, even though the same brain structures and connected neural circuits are important for the two different functionalities. Motivated by experimental results from both fields, we use theoretical modeling to describe the coupled dynamics of sleep and navigation circuits and propose a rationale for why they interact. The resulting model can incorporate and explain several experimental findings about sleep and navigation in flies and mice. The model is based on a ring attractor network which is combined with plasticity rules that change between sleep and wake phases and shows autonomous dynamics during sleep, reminiscent of observations in the head direction system of mice
Scalable, Time-Responsive, Digital, Energy-Efficient Molecular Circuits using DNA Strand Displacement
We propose a novel theoretical biomolecular design to implement any Boolean
circuit using the mechanism of DNA strand displacement. The design is scalable:
all species of DNA strands can in principle be mixed and prepared in a single
test tube, rather than requiring separate purification of each species, which
is a barrier to large-scale synthesis. The design is time-responsive: the
concentration of output species changes in response to the concentration of
input species, so that time-varying inputs may be continuously processed. The
design is digital: Boolean values of wires in the circuit are represented as
high or low concentrations of certain species, and we show how to construct a
single-input, single-output signal restoration gate that amplifies the
difference between high and low, which can be distributed to each wire in the
circuit to overcome signal degradation. This means we can achieve a digital
abstraction of the analog values of concentrations. Finally, the design is
energy-efficient: if input species are specified ideally (meaning absolutely 0
concentration of unwanted species), then output species converge to their ideal
concentrations at steady-state, and the system at steady-state is in (dynamic)
equilibrium, meaning that no energy is consumed by irreversible reactions until
the input again changes.
Drawbacks of our design include the following. If input is provided
non-ideally (small positive concentration of unwanted species), then energy
must be continually expended to maintain correct output concentrations even at
steady-state. In addition, our fuel species - those species that are
permanently consumed in irreversible reactions - are not "generic"; each gate
in the circuit is powered by its own specific type of fuel species. Hence
different circuits must be powered by different types of fuel. Finally, we
require input to be given according to the dual-rail convention, so that an
input of 0 is specified not only by the absence of a certain species, but by
the presence of another. That is, we do not construct a "true NOT gate" that
sets its output to high concentration if and only if its input's concentration
is low. It remains an open problem to design scalable, time-responsive,
digital, energy-efficient molecular circuits that additionally solve one of
these problems, or to prove that some subset of their resolutions are mutually
incompatible.Comment: version 2: the paper itself is unchanged from version 1, but the
arXiv software stripped some asterisk characters out of the abstract whose
purpose was to highlight words. These characters have been replaced with
underscores in version 2. The arXiv software also removed the second
paragraph of the abstract, which has been (attempted to be) re-inserted.
Also, although the secondary subject is "Soft Condensed Matter", this
classification was chosen by the arXiv moderators after submission, not
chosen by the authors. The authors consider this submission to be a
theoretical computer science paper
Electron-phonon scattering in quantum point contacts
We study the negative correction to the quantized value of the
conductance of a quantum point contact due to the backscattering of electrons
by acoustic phonons. The correction shows activated temperature dependence and
also gives rise to a zero-bias anomaly in conductance. Our results are in
qualitative agreement with recent experiments studying the 0.7 feature in the
conductance of quantum point contacts.Comment: 4 pages, no figure
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