Recursos de colección

Caltech Authors (162.509 recursos)

Repository of works by Caltech published authors.

Type = Conference or Workshop Item

Mostrando recursos 1 - 20 de 283

  1. Measuring the Robustness of Neural Networks via Minimal Adversarial Examples

    Dathathri, Sumanth; Zheng, Stephan; Gao, Sicun; Murray, Richard M.
    Neural networks are highly sensitive to adversarial examples, which cause large output deviations with only small input perturbations. However, little is known quantitatively about the distribution and prevalence of such adversarial examples. To address this issue, we propose a rigorous search method that provably finds the smallest possible adversarial example. The key benefit of our method is that it gives precise quantitative insight into the distribution of adversarial examples, and guarantees the absence of adversarial examples if they are not found. The primary idea is to consider the nonlinearity exhibited by the network in a small region of the input...

  2. Studies of the large-scale structure in adiabatic and moderately-wall-heated subsonic boundary layers

    Gordeyev, Stanislav; Smith, Adam E.; Saxton-Fox, Theresa; McKeon, Beverley
    Simultaneous velocity-optical measurements in subsonic boundary layers were conducted in order to investigate the relationship between the instantaneous 2-D wavefronts, measured by different optical sensors, the Malley probe and 2-D Shack-Hartmann sensors, and the instantaneous large-scale structure along a wall-normal plane, using PIV in both incompressible and compressible subsonic boundary layers. These systematic studies of the instantaneous relation between the large-scale boundary layer structure and its aero-optical signature provide additional understanding of the instantaneous dynamics of the large-scale structure at subsonic and transonic speeds.

  3. Modeling momentum and scalar transport in a wall-bounded turbulent flow

    Saxton-Fox, Theresa; McKeon, Beverley
    A mildly-heated turbulent boundary layer was studied to characterize the relationship between velocity structures and the scalar field. Particle image velocimetry (PIV) and a Malley probe (Malley et al., 1992) were used to simultaneously measure the velocity field and the streamwise gradients of the scalar field (Gordeyev et al., 2014) respectively. Two distinct velocity scales were identified to be correlated to scalar mixing by conditionally averaging the velocity field on the existence of a scalar gradient. Resolvent analysis was used to create simple models of these velocity scales (McKeon and Sharma, 2010) and to probe their interaction. Using a combination...

  4. Scale interactions and 3D critical layers in wall-bounded turbulent flows

    Saxton-Fox, Theresa; McKeon, Beverley
    Phenomena related to scale interaction in wall-bounded turbulent flows were considered through the lens of critical layer analysis. A 3D critical layer formulation was used, with the 3D critical layer associated with a particular structure defined as the height where the instantaneous velocity field composed of the large scales and the mean velocity matched the convection velocity of that structure. Characterization of the velocity field surrounding the 3D critical layer in wall-bounded turbulent flows led to conclusions consistent with previously observed phenomena including the shape of the interface defining uniform momentum zones (UMZs) [1] [2] and amplitude modulation of the...

  5. Annotated Reconstruction of 3D Spaces Using Drones

    Nair, Suraj; Ramachandran, Anshul; Kundzicz, Peter
    As the fields of robotics and drone technologies are continually advancing, the challenge of teaching these agents to learn and maneuver in the real world becomes increasingly important. A critical component of this is the ability for a robot to map and understand its surrounding unknown environment, both in terms of physical structure and object classification. In this project we tackle the challenge of mapping a 3D space with annotations using only 2D images acquired from a Parrot Drone. In order to make such a system operate efficiently in close to real time, we address a number challenges including (1)...

  6. Parallelizing Synthesis from Temporal Logic Specifications by Identifying Equicontrollable States

    Dathathri, Sumanth; Filippidis, Ioannis; Murray, Richard M.
    For the synthesis of correct-by-construction control policies from temporal logic specifications the scalability of the synthesis algorithms is often a bottle- neck. In this paper, we parallelize synthesis from specifications in the GR(1) frag- ment of linear temporal logic by introducing a hierarchical procedure that allows decoupling of the fixpoint computations. The state space is partitioned into equicontrollable sets using solutions to parametrized games that arise from decomposing the original GR(1) game into smaller reachability-persistence games. Following the partitioning, another synthesis problem is formulated for composing the strategies from the decomposed reachability games. The formulation guarantees that com- posing the...

  7. Aggregation of Nontuberculous Mycobacteria in Vitro and in Situ

    DePas, W.; Bergkessel, M.; Newman, D. K.
    The incidence of nontuberculous mycobacterial (NTM) infections in cystic fibrosis (CF) patients is increasing, with some CF clinics in the US reporting NTM prevalence upwards of 25%. In addition, the current treatment regimen for NTM involves long courses of antibiotic cocktails that demonstrate limited efficacy and cause frequent and serious side effects. Mycobacterium abscessus, in particular, is difficult to treat and correlates with a more rapid decline in lung function compared to Mycobacterium avium complex. Studies with zebrafish and human cell cultures have demonstrated that M. abscessus is more virulent when aggregated into cord-like biofilms, in part because of the decreased ability...

  8. Total synthesis and study of myrmicarin alkaloids

    Ondrus, Alison Evelynn; Movassaghi, Mohammad
    A convergent total synthesis of myrmicarin alkaloids and related derivatives based on a potentially biomimetic dimerization of optically active pyrroloindolizines is described. A variety of dimerization strategies are discussed that take advantage of the unique chemistry of pyrroloindolizines. Mechanistic insights regarding the high level of substrate directed stereoselection in these dimerization reactions will be discussed.

  9. Twists and turns of lactam research

    Stoltz, Brian M.
    The importance of the amide bond cannot be overstated. Typical amides are planar structures, however, amide bonds can be highly twisted such as in bicyclic bridgehead lactams. The distortion of the orbitals from planarity and the pyramidalization of the nitrogen from sp toward sp dramatically affect the stability and reactivity of anti-Bredt amides. In 2006, our group published the first unambiguous synthesis and characterization of 2- quinuclidonium tetrafluoroborate. Since then we have been fascinated with the synthesis and characterization of such strained reactive lactams. We have also pursued the synthesis of a series of novel stereogenic lactams that can be employed as intermediates in multi-step synthesis....

  10. Fully quantum simulation of surface enhanced Raman scattering from real-time ab-initio methods

    Kretchmer, Joshua; Chan, Garnet
    Surface enhanced Raman scattering (SERS) is the huge enhancement of the Raman signal of a mol. near a metal or nanoparticle surface due to coupling with the plasmon of the metal nanostructure. Although SERS was discovered several decades ago, a complete picture of the underlying mechanism still remains elusive due to the difficulty of treating the coupled metal-mol. system fully quantum mech.; the majority of previous studies have treated the plasmon classically accounting for only an electromagnetic enhancement of the Raman signal. However, it is well known that the SERS enhancement can be orders of magnitude larger than that predicted by electromagnetic enchancement....

  11. Improving thermodynamics teaching for chemistry students

    Yu, Ted
    Thermodn. is an important subject matter covered in first year physics and chem. It is also one of the required upper-level courses in subjects like Chem., Mech. Engineering, Materials Engineering, and Chem. Engineering. Due to the traditionally math. nature of this course, the use of "atomistic" visual aids can greatly enhance a chem. student's learning of this subject. By introducing the simple concept of the quantum vol. (QV) of a gas atom first, the idea is to start thermodn. from an atomistic point of view. The QV is the amt. of vol. that an atom's wavelength occupies derived from the cube of the DeBroglie Wavelength....

  12. Volatile nematode sex pheromones

    Shinya, Ryoji; Gronquist, Mathew; Leighton, Daniel; Hsueh, Yen-Ping; Schroeder, Frank; Sternberg, Paul
    Nematodes produce a staggering array of sol. social cues, glycosides of dideoxy-sugars such as the ascarylose (ascarosides), that are secondary metabolites and communicate information such as population d. and location of sex partners. We found that predatory fungi respond to certain ascarosides by making sticky traps that trap and kill nematodes. This finding suggested that one driver of the evolution of ascaroside prodn. is avoiding predation. We have recently identified using GC-MS of the head-space of cultures of two distant genera of nematodes - the fungal-feeding and tree-parasitic Bursaphelenchus and the fruit-assocd., free-living Caenorhabditis - a set of volatile compds. that are produced by nematodes and...

  13. Synthesis and evaluation of dithiolate-modified ruthenium olefin metathesis catalysts

    Montgomery, Timothy; Grubbs, Robert
    A premier method for the formation of carbon-carbon double bonds, olefin metathesis has found widespread use in synthetic org., biol., and materials chem. Recent advancements made using ruthenium olefin metathesis catalysts have employed dithiolate X-type ligands, giving rise to a kinetically (E)-selective olefin metathesis process through stereoretention of the starting olefin geometry. Modification of the dithiolate ligands provides a path to metathesis catalysts contg. interesting electronic and stereochem. properties. These catalysts deliver a better understanding of the structure-activity relationships obsd. in olefin metathesis catalysts.

  14. Synthesis and evaluation of dithiolate-modified ruthenium olefin metathesis catalysts

    Montgomery, Timothy; Grubbs, Robert
    A premier method for the formation of carbon-carbon double bonds, olefin metathesis has found widespread use in synthetic org., biol., and materials chem. Recent advancements made using ruthenium olefin metathesis catalysts have employed dithiolate X-type ligands, giving rise to a kinetically (E)-selective olefin metathesis process through stereoretention of the starting olefin geometry. Modification of the dithiolate ligands provides a path to metathesis catalysts contg. interesting electronic and stereochem. properties. These catalysts deliver a better understanding of the structure-activity relationships obsd. in olefin metathesis catalysts.

  15. Degradation and mineralization of common pharmaceuticals using nitrogen-doped carbon monolith 3D electrode with 3D printed electrochemical reactor

    Liu, Kai; Yu, Menglin; Jasper, Justin; Hoffmann, Michael
    The oxidative degrdn. of common pharmaceuticals including propranolol, carbamazepine, ranitidine, metoprolol, trimethoprim, cimetidine, ciprofloxacin, and acetaminophen have been studied by using nitrogendoped carbon monolith 3D cathode in a continuous electro-peroxone process with novel 3D printed electrochem. reactor. The carbon monolith electrode was prepd. from polymer precursor with the ease of control over nitrogen dopant concn. and structure of the 3D porosity, which tunes oxygen redn. selectivity to facilitate hydrogen peroxide prodn. and improves mass transfer resp. The effect of parameters including c.d., soln. pH, and flow rate on the pharmaceutical degrdn. in aq. soln. was detd. The mineralization of pharmaceuticals and...

  16. Direct simulation of non-adiabatic dynamics in large-scale enzymatic systems

    Kretchmer, Joshua; Miller, Thomas
    The simulation of general non-adiabatic processes, such as electron transfer, proton-transfer, and protoncoupled electron transfer, in enzymic systems presents a challenge for theor. methods due to the large system-sizes, the coupling between classical and quantum mech. motions, and the multiple time-scales present in these systems. To address these challenges we have developed the kinetically-constrained ring-polymer mol. dynamics (KC-RPMD) method for the direct simulation of non-adiabatic processes in large-scale biol. and chem. systems. KC-RPMD, like the conventional ring-polymer mol. dynamics (RPMD), is based on Feynman's path-integral formulation of statistical mechanics and is able to simulate quantum dynamical processes using purely classical dynamics; KC-RPMD goes...

  17. Cellular structural biology probing prokaryotic and eukaryotic membrane protein complexes in-situ at atomic resolution

    Kaplan, Mohammed
    Cellular structural biol. aims at studying the structure and dynamics of biomols. at at. resoln. in their physiol. settings. Over the past few decades, solid-state NMR (ssNMR) has proven to be a powerful technique that can provide at.-resoln. information on membrane proteins in different lipid environments. Recently, such studies have been extended to include small membrane proteins in native milieu. However, larger complexes pose further challenges in terms of sample prepn., data anal. and sensitivity. Here, we show that sensitivity-enhanced ssNMR through Dynamic Nuclear Polarization (DNP) can be used to investigate large prokaryotic and eukaryotic membrane protein complexes in-situ at at....

  18. Cellular structural biology probing prokaryotic and eukaryotic membrane protein complexes in-situ at atomic resolution

    Kaplan, Mohammed
    Cellular structural biol. aims at studying the structure and dynamics of biomols. at at. resoln. in their physiol. settings. Over the past few decades, solid-state NMR (ssNMR) has proven to be a powerful technique that can provide at.-resoln. information on membrane proteins in different lipid environments. Recently, such studies have been extended to include small membrane proteins in native milieu. However, larger complexes pose further challenges in terms of sample prepn., data anal. and sensitivity. Here, we show that sensitivity-enhanced ssNMR through Dynamic Nuclear Polarization (DNP) can be used to investigate large prokaryotic and eukaryotic membrane protein complexes in-situ at at....

  19. Noncovalent modulation of protien energy landscapes with targeted molecular binders

    Bunck, David; Atsavapranee, Beatriz; Museth, Katrine; Vander Velde, David; Heath, James
    Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease caused by the deterioration of motor neurons that abates essential biol. functions and exhibits survival times of 3 - 5 years after diagnosis. One driver of this disease derives from inherited mutations to the protein superoxide dismutase 1 (SOD1), which hinder proper folding and result in the accumulation of toxic aggregates. We identified cyclic peptides that target precise epitopes on SOD1 through an emerging screening platform that furnishes high-affinity binders against regions of a protein independent of secondary and tertiary structure. Binding these epitopes both stabilizes the native state and accelerates folding. In this context, these small peptides...

  20. Noncovalent modulation of protien energy landscapes with targeted molecular binders

    Bunck, David; Atsavapranee, Beatriz; Museth, Katrine; Vander Velde, David; Heath, James
    Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease caused by the deterioration of motor neurons that abates essential biol. functions and exhibits survival times of 3 - 5 years after diagnosis. One driver of this disease derives from inherited mutations to the protein superoxide dismutase 1 (SOD1), which hinder proper folding and result in the accumulation of toxic aggregates. We identified cyclic peptides that target precise epitopes on SOD1 through an emerging screening platform that furnishes high-affinity binders against regions of a protein independent of secondary and tertiary structure. Binding these epitopes both stabilizes the native state and accelerates folding. In this context, these small peptides...

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