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Caltech Authors (96,904 recursos)
Repository of works by Caltech published authors.

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Mostrando recursos 1 - 20 de 4,010

1. An Electronic Photoreceptor Sensitive to Small Changes in Intensity - Delbrück, T.; Mead, C. A.
We describe an electronic photoreceptor circuit that is sensitive to small changes in incident light intensity. The sensitivity to changes in the intensity is achieved by feeding back to the input a filtered version of the output. The feedback loop includes a hysteretic element. The circuit behaves in a manner reminiscent of the gain control properties and temporal responses of a variety of retinal cells, particularly retinal bipolar cells. We compare the thresholds for detection of intensity increments by a human and by the circuit. Both obey Weber's law and for both the temporal contrast sensitivities are nearly identical.

2. Sequence-Controlled Polymers by Ruthenium-Mediated Ring-Opening Metathesis Polymerization - Chang, Alice B.; Miyake, Garret M.; Grubbs, Robert H.
In sequence-controlled polymers, repeat units of different chemical composition are arranged in a well-defined order. Due to its living characteristics and functional group tolerance, ruthenium-mediated ring-opening metathesis polymerization (ROMP) is a powerful strategy for sequence control. Catalysts for ROMP can be tuned to achieve polymers with highly controlled sequences, thereby encoding structural information in the structure of the catalyst itself. The study of sequence-cotrolled polymerization offers both mechanistic insights and routes to new materials with precise structure–property relationships. This chapter will review design strategies for ruthenium-mediated sequence-controlled ROMP. Structural control in terms of cis/trans-selectivity and tacticity will first be discussed to illustrate the key principles of catalyst design. This framework will then be extended...

3. A Handheld Magnetic Sensing Platform for Antigen And Nucleic Acid Detection - Pai, A.; Khachaturian, A.; Chapman, S.; Hu, A.; Wang, H.; Hajimiri, A.
The core requirements for point-of-care (POC) diagnostics necessitate low-cost, high multiplexing, portability, easily integrated sample preparation, and quick measurement time [1, 2]. Frequency-shift based magnetic sensing is a measurement technique utilizing a complementary metal-oxide-semiconductor (CMOS) integrated-circuit (IC) chip for magnetic label detection. Using this technology, we have developed a complete handheld, low-power, low-cost, disposable cartridge-based diagnostic device (Fig. 1a,b) with two fully implemented assays for antigens and nucleic acids. We have demonstrated reliable measurements down to 100 pM for a 31 base-pair oligomer and 1 pM for the protein interferon-γ (IFN-γ).

4. On-Chip Fluorescence Microscopy for Wide Field-of-View High-Throughput Phynotype Screening of Caenorhabditis elegans - Han, Chao; Pang, Shuo; Kato, Mihoko; Sternberg, Paul; Yang, Changhuei
We developed a low-cost compact on-chip fluorescence imaging platform, termed the Fluorescence Talbot Microscopy (FTM), which utilizes the Talbot self-imaging effect to enable efficient fluorescence imaging over a large and directly-scalable field-of-view (FOV). The FTM prototype has a resolution of 1.2 μm and an FOV of 3.9×3.5mm^2. We demonstrate the use of the FTM prototype in performing high-throughput imaging of live Caenorhabditis elegans (C. elegans), and RNA interference (RNAi) phenotyping of distal tip cell (DTC) migration defects in C. elegans.

5. Contention Resolution under Selfishness - Christodoulou, George; Ligett, Katrina; Pyrga, Evangelia
In many communications settings, such as wired and wireless local-area networks, when multiple users attempt to access a communication channel at the same time, a conflict results and none of the communications are successful. Contention resolution is the study of distributed transmission and retransmission protocols designed to maximize notions of utility such as channel utilization in the face of blocking communications. An additional issue to be considered in the design of such protocols is that selfish users may have incentive to deviate from the prescribed behavior, if another transmission strategy increases their utility. The work of Fiat et al. [8] addresses this issue by constructing an asymptotically optimal incentive-compatible...

6. Cosmic Rays - Mewaldt, R. A.
Cosmic rays are high energy charged particles, originating in outer space, that travel at nearly the speed of light and strike the Earth from all directions. Most cosmic rays are the nuclei of atoms, ranging from the lightest to the heaviest elements in the periodic table. Cosmic rays also include high energy electrons, positrons, and other subatomic particles. The term "cosmic rays" usually refers to galactic cosmic rays, which originate in sources outside the solar system, distributed throughout our Milky Way galaxy. However, this term has also come to include other classes of energetic particles in space, including nuclei and electrons accelerated in association with energetic events on the Sun...

7. Implications of 26-Day Variations for the Global Modulation - Zhang, M.; Simpson, J. A.; Kunow, H.; Jokipii, J. R.; Potgieter, M. S.; Burger, R.A.; Cummings, A. C.

8. Slip Along the San Andreas Fault Associated with the Earthquake - Sieh, Kerry E.
Some of the fault slip associated with the 1979 Imperial Valley earthquake occurred along other than the Imperial fault and the Brawley fault zone. More than 90 km to the north of the seismogenic fault, a 39-km-long section of the San Andreas fault developed a discontinuous set of surficial fractures soon after the earthquake. This set of fractures consisted of small left-stepping echelon cracks displaying extensional and dextral components of movement. Average dextral slip was about 4 mm, and slip reached 10 mm at one point along the fault. In one locality the cracks formed between Va and 4Vfe days after the main shock, although slippage at depth may...

9. Aftershocks and Preearthquake Seismicity - Johnson, Carl E.; Hutton, L. K.
Although primary surface faulting was mapped for nearly 30 km, aftershocks extended in a complex pattern more than 100 km along the trend of the Imperial fault. A first-motion focal mechanism for the main shock is consistent with right-lateral motion on a vertical fault striking N. 42° W., in agreement with the strike of the Imperial fault within the limits of resolution. There is evidence that conjugate faulting on a buried complementary northeast-trending structure occurred at the north limit of displacement on the Imperial fault near Brawley, Calif. This faulting was apparently initiated at the time of a magnitude 5.8 aftershock 8 hours after the main shock. A line...

10. Preearthquake and Postearthquake Creep on the Imperial Fault and the Brawley Fault Zone - Cohn, Stephen N.; Allen, Clarence R.; Gilman, Ralph; Goulty, Neil R.
Taken together, 12 years of alinement-array data, 4 years of creepmeter records from four instruments, and 2 years of surveys from two nail files suggests that creep events on the Imperial fault 2 to 5 months before the October 15 earthquake are consistent with longterm trends and not indicative of any imminent event. No discernible creep occurred on the fault in the hours and days before the earthquake. Records of coseismic displacement imply that response of the soil to the fault slip at depth was brittle rather than plastic; they uniquely demonstrate that the minimum rate of surface fault displacement was 1.8 cm/s. Continuing measurements of afterslip show that all...

11. Approximate Sorting of Data Streams with Limited Storage - Farnoud (Hassanzadeh), Farzad; Yaakobi, Eitan; Bruck, Jehoshua
We consider the problem of approximate sorting of a data stream (in one pass) with limited internal storage where the goal is not to rearrange data but to output a permutation that reflects the ordering of the elements of the data stream as closely as possible. Our main objective is to study the relationship between the quality of the sorting and the amount of available storage. To measure quality, we use permutation distortion metrics, namely the Kendall tau and Chebyshev metrics, as well as mutual information, between the output permutation and the true ordering of data elements. We provide bounds...

12. Past, Present, and Future Cosmic Ray Identification Applications for Large Area Silicon Detectors - Walton, J. T.; Lee, J. S.; Lewak, D.; Wong, Y. K.; Cummings, A. C.; Mewaldt, R. A.; Wiedenbeck, M. E.; Knowlton, W. B.; Haller, E. E.
An overview of the application of Si(Li) detectors to cosmic-ray identification is presented. A vacancy-related defect in FZ silicon that can limit the lithium compensation process in Si(Li) detector fabrication is discussed and a gettering process to remove this defect is outlined. Computer simulation of the gettering process is shown to yield native point defect diffusivity and concentration values approaching those recently proposed by Gösele, Plöβl and Tan.

13. Design of a Frequency Shift Based CMOS Magnetic Sensor Array for Point-of-Care (PoC) Biomolecular Diagnosis Applications - Wang, Hua; Hajimiri, Ali
Future point-of-care (PoC) molecular-level diagnostic systems require advanced biosensors that can offer high sensitivity, ultra-portability, and a low price-tag. Targeting on-site detection of biomolecules, such as DNAs, RNAs, or proteins, this type of systems is believed to play a crucial role in a variety of emerging applications such as in-field medical diagnostics, epidemic disease control, and biohazard detection.

14. Hard X-ray Imaging Survey of the Galactic Plane with the Caltech Gamma-Ray Imaging Payload GRIP-2 - Corbel, S.; Cook, W. R.; Harrison, P. F.; Prince, Thomas A.; Schindler, S. M.; Wang, S.
In a recent balloon flight on October 6-7, 1995, the Caltech coded aperture Gamma-Ray Imaging Payload (GRIP-2) imaged numerous fields in the Galactic plane and center in the 25 ke V - 600 ke V energy band. GRIP-2's large phoswich detector (3830 cm2), 15° (FWHM) field of view, 30' angular resolution and 6' point source localization ability make it ideally suited for surveying the accreting binary population of the Galaxy at high energy. We present a brief description of the instrument and we also report preliminary imaging results from our recent Southern hemisphere campaign and show the capabilities of this balloon-borne coded...

15. Development of Grazing Incidence Multilayer Mirrors for Hard X-ray Focusing Telescopes - Mao, Peter H.; Harrison, Fiona A.; Platonov, Y.Y.; Broadway, D.; DeGroot, B.; Christensen, F. E.; Craig, William W.; Hailey, C. J.
We are developing depth-graded, multilayer-coated mirrors for astrophysical hard X-ray focusing telescopes. In this paper, we discuss the primary technical challenges associated with the multilayer coatings, and report on progress to date. We have sputtered constant cl-spacing and depth-graded W / Si multilayers onto 0.3- 0.5 mm thick DURAN glass (AF45 and D263) and 0.4 mm thick epoxy replicated aluminum foils (ERAFs) , both of which are potential mirror substrates. We have characterized the interfacial roughness, uniformity, and stress of the coatings. The average interfacial roughness of each multilayer was measured from specular reflectivity scans (Bi = Br) using Cu K0 X-rays. The thin film...

16. Discussion on “phenomenological modeling: Present and future” - Smits, Alexander J.; Stull, Roland; Coantic, Michel; Traugott, Stephen; Mathieu, Jean; Shih, Tsan-Hsing; Narasimha, Roddam; Launder, Brian; El Tahry, Sherif; Rodi, Wolfgang; Reynolds, Bill; George, Bill; Roshko, Anatol; Bilger, Bob; Herring, Jack; Speziale, Charles; Nagib, Hassan; Cantwell, Brian; Wyngaard, John; Bradshaw, Peter; Lumley, John
This afternoon all of the models that we have heard fall in the same class; namely, local closures. First-order local closure (K-theory or eddy diffusivity) models the momentum fluxes as down-gradient of the mean momentum. The second-order local closure models the third moments as down-gradient of the local second moments, or local mean variables. There is another completely different class of modeling or class of closure, and that is non-local turbulence closure. I mentioned before about the transilient matrix that describes the mixing between different points separated a finite distance in space. One can parameterize this matrix in terms of mean flow state or mean flow instability. When you do...

17. Phenomenological modeling: Present and future. Comment 1 - Roshko, A.
Professor Launder's position paper on phenomenological modelling is an impressive survey and valuable account of the status of second-moment closure, principally as applied to Reynolds Stresses. In this respect, it supplements and updates the monograph of Professor Rodi (1980), in which the emphasis is on the status of first-order closures, in particular the κ-ε model, as of 10 years ago. Between them the two works provide an excellent reference source containing the equations; the rationale for modelling decisions that are made; tables of the constants that have been selected; displays of flow computations and their comparison with experimental measurements for a varied number of flows; and extensive reference lists.

18. Discussion on the utility of dynamical systems approach - Aubry, Nadine; Perry, Tony; Lumley, John; Holmes, Philip; Frisch, Uriel; Sudan, Ravi; Moffatt, Keith; Phillips, Bill; Marsden, Jerry; George, Bill; Roshko, Anatol; Hussain, Fazle; Reynolds, Bill; Leonard, Tony; Moin, Parviz
I have a rather provocative question to ask the speakers. What I am wondering is: When you apply the proper orthogonal decomposition - I know this is a procedure you use and it is probably standard - you remove the mean flow and you only look at the perturbations. Why do not you include the mean flow, because if you did you would suppress the cubic terms, and also you would be getting something that would be closer to what people call coherent structures, such as hairpin vortices.

19. Live Cell Imaging of the Cytoskeleton and Cell Wall Enzymes in Plant Cells - Sampathkumar, Arun; Wightman, Raymond
The use of live imaging techniques to visualize the dynamic changes and interactions within plant cells has given us detailed information on the function and organization of the cytoskeleton and cell wall associated proteins. This information has grown with the constant improvement in imaging hardware and molecular tools. In this chapter, we describe the procedure for the preparation and live visualization of fluorescent protein fusions associated with the cytoskeleton and the cell wall in Arabidopsis.

20. Panel Discussion: Direct Numerical Simulation or Experiments? - Roshko, A.; Kleiser, L.; Moin, P.
I have been tapped as the moderator for this panel, and I hope that everybody else is prepared to say a few things. I think that our job as panellists is to provoke a little discussion from the audience, and I would like to say a few words to get things started. First, to clarify the subject of the discussion a little bit, I think that what is implied in the title by "experiments" are laboratory experiments. I think that the direct numerical simulations are, in fact, also experiments, and that we should be talking about using direct numerical simulation in the same way that...

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