Repository of works by Caltech published authors.
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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.
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...
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).
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.
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.  addresses
this issue by constructing an asymptotically optimal incentive-compatible...
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...
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...
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...
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
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...
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.
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...
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...
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...
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
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.
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.
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...