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Caltech Authors (91,350 recursos)
Repository of works by Caltech published authors.

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Mostrando recursos 1 - 20 de 35,451

1. A Hox regulatory network of hindbrain segmentation is conserved to the base of vertebrates - Parker, Hugo J.; Bronner, Marianne E.; Krumlauf, Robb
A defining feature governing head patterning of jawed vertebrates is a highly conserved gene regulatory network that integrates hindbrain segmentation with segmentally restricted domains of Hox gene expression. Although non-vertebrate chordates display nested domains of axial Hox expression, they lack hindbrain segmentation. The sea lamprey, a jawless fish, can provide unique insights into vertebrate origins owing to its phylogenetic position at the base of the vertebrate tree. It has been suggested that lamprey may represent an intermediate state where nested Hox expression has not been coupled to the process of hindbrain segmentation. However, little is known about the regulatory network...

2. Damped Fourier spectrum and response spectra - Udwadia, F. E.; Trifunac, M. D.
This paper describes the physical relationships that exist between the Fourier transform and the response spectrum of a strong-motion accelerogram. By developing the new concept of the “Damped Fourier Spectrum” (D.F.S.), we show that the velocity and displacement of the damped oscillator can be represented by a linear combination of the real and imaginary parts of the D.F.S. and by the initial conditions. The D.F.S. represents a new way of “smoothing” the classical Fourier Transform by using a physically based filter.

3. Vertical profile of lead isotopic compositions in the north-east Pacific - Flegal, A. R.; Itoh, K.; Patterson, C. C.; Wong, C. S.
Ratios of lead isotopes (^(204)Pb, ^(206)Pb, ^(207)Pb and ^(208)Pb) may be used to distinguish leads from different sources in sea water in a manner similar to neodymium isotopes. The following data from the north-east Pacific include the first vertical profile measurements of lead isotopic compositions in sea water. These preliminary data indicate that lead in offshore (48° N, 141° W) north-east Pacific surface waters (^(206)Pb/^(207)Pb = 1.164) was derived from aeolian inputs of Asian (Japanese) industrial leads (^(206)Pb/^(207)Pb = 1.160) (M. Murozumi, personal communication), but that lead in water immediately (400 m) below it (^(206)Pb/^(207)Pb = 1.211) was derived from...

4. Earthquake prediction - Allen, Clarence R.
Five to ten years ago, great optimism existed in the seismological community that routine short-term earthquake prediction was imminent, based mainly on reported successes in various parts of the world in identifying physical precursors to earthquakes. Especially significant was the successful Chinese prediction of the 1975 Haicheng earthquake, with considerable saving of lives. Within the past five years, however, research results have been sobering, and the problem turns out to be a more difficult one than we had thought. In no part of the world has a successful, routinely operating earthquake-prediction system yet been implemented.

5. Seismicity of the Garlock fault, California - Astiz, Luciana; Allen, Clarence R.
The Garlock fault is a 265-km-long left-slip fault striking northeastward from the San Andreas fault in southern California. Relocations of earthquakes that occurred from 1932 to 1981 on and near this major fault were made using the master-event technique. The spatial distribution of seismicity along the fault is different west and east of its midpoint near Rand, where the largest en-echelon offset and a marked change in strike occur. These two segments also display distinct geologic features and different seismic and aseismic behavior. The 150-km-long segment west of Rand has shown continuous low seismic activity during the past 50 yr,...

6. Waves of accelerated motion in a glacier approaching surge: the mini-surges of Variegated Glacier, Alaska, U.S.A. - Kamb, Barclay; Engelhardt, Hermann
Periods of dramatically accelerated motion, in which the flow velocity increases suddenly from about 55 cm/d to a peak of 100-300 cm/d and then decreases gradually over the course of a day, occurred repeatedly during June and July 1978-81 in Variegated Glacier (Alaska), a surging-type glacier that surged in 1982-83. These "mini-surges" appear to be related mechanistically to the main surge. The flow-velocity peak propagates down-glacier as a wave at a speed of about 0.3 km/h, over a reach of about 6 km in length. It is accompanied by a propagating pressure wave in the basal water system of the...

7. Local distribution of strong earthquake ground motions - Hudson, Donald E.
Twenty ground stations distributed over a 40-square-mile area in Pasadena recorded strong ground shaking during the San Fernando earthquake of February 9, 1971. Relative responses at 10 of these same stations as measured for small earthquakes by standard Wood-Anderson torsion seismometers are available for comparison from a study made by Gutenberg in the 1950's. Frequency spectra of strong ground motions as calculated for four sites having time-recording accelerographs assist in the interpretation of seismoscope results at the other stations. Attempts to correlate local distributions with known features of local geology such as thickness of alluvium, distance from known faults, etc.,...

8. A perturbation scheme for obtaining partial derivatives of Love-wave group-velocity dispersion - Kosloff, Dan
A method is derived for obtaining partial derivatives of Love-wave group-velocity spectra for a layered medium using a second-order perturbation theory. These partials are a prerequisite for systematic inversion of group-velocity spectra but they are helpful as well in trial and error methods. Mathematically the equation of motion and boundary conditions for Love waves are a singular Sturm Liouville type eigenvalue problem. In the case of a fixed wave number, the eigenvalues are the negative of the square of the frequencies. Thus, by expressing the first- and second-order perturbations of the eigenvalues in terms of partial derivatives of the frequency...

9. Physical Properties of the Atmosphere up to 100 km - Gutenberg, B.
Results of new calculations of temperature, pressure, density, and other physical quantities in the stratosphere up to an elevation of 100 km are given and discussed.

10. Earthquakes and structure in southern California - Gutenberg, Beno
During recent years the accuracy in determining the arrival times of earthquake waves in southern and central California has been notably improved, so that more detailed results concerning the structure of the earth's crust in California are to be expected from the study of such records. Fifty shocks were selected, and their epicenters, depths of foci, origin times, and magnitudes determined and discussed. All known corrections have been applied; in particular, the effect of the altitude of some of the stations is beyond the probable error of the readings. With this improved material it is possible not only to investigate...

11. A Conversation with Frank Press - Goodstein, Judith R.
Geophysicist Frank Press was director of Caltech’s Seismological Laboratory from 1957 to 1965. In this interview, he recalls his work with Maurice Ewing at Columbia’s Lamont Geological Observatory; his directorship of Caltech’s Seismological Laboratory and colleagues Charles Richter, Beno Gutenberg, and Hugo Benioff; his work on the free oscillations of the earth; and his part in establishing the worldwide network of seismographs for the detection of nuclear weapons testing.

12. Stress-gradient coupling in glacier flow: IV. Effects of the "T" term - Kamb, Barclay; Echelmeyer, Keith A.
The "T term" in the longitudinal stress equilibrium equation for glacier mechanics, a double y-integral of ∂^2T_(xy)/∂x^2 where x is a longitudinal coordinate and y is roughly normal to the ice surface, can be evaluated within the framework of longitudinal flow-coupling theory by linking the local shear stress T_(xy) at any depth to the local shear stress T_B at the base, which is determined by the theory. This approach leads to a modified longitudinal flow-coupling equation, in which the modifications deriving from the T term are as follows: 1. The longitudinal coupling length I is increased by about 5%. 2. The asymmetry parameter σ...

13. Stress-gradient coupling in glacier flow: III. Exact longitudinal equilibrium equation - Kamb, Barclay
The "vertically" integrated, exact longitudinal stress-equilibrium equation of Budd (1970) is developed further in. such a way as to yield an equation that gives explicitly and exactly the contributions to the basal shear stress made by surface and bed slope, surface curvature, longitudinal stress deviators, and longitudinal stress gradients in a glacier flowing in plane strain over a bed of longitudinally varying slope. With this exact equation, questions raised by various approximate forms of the longitudinal equilibrium equation can be answered decisively, and the magnitude of errors in the approximations can be estimated. To first order, in the angle δ that describes fluctuations in the surface slope...

14. Low-Velocity Layers in the Earth, Ocean, and Atmosphere - Gutenberg, Beno
These layers increase the difficulty of locating buried explosions and may cause sonar booms.

15. Seismological evidence for roots of mountains - Gutenberg, Beno
Theoretical problems concerned with the calculation of the velocities of seismic waves in the various layers of the earth's crust, and the determination of the thickness of such layers, are discussed. The results are applied to seismograms obtained from artificial explosions, and sources of error in interpretation are investigated. Seismograms registered in different parts of the earth from epicenters less than 1000 km from stations are used to investigate the layering in these regions and the problem of mountain roots. The bearing of the findings on the theory of isostasy is discussed.

16. Measurement of WZ and ZZ production in pp collisions at √s = 8 TeV in final states with b-tagged jets - Chatrchyan, S.; Apresyan, A.; Bornheim, A.; Bunn, J.; Chen, Y.; Di Marco, E.; Duarte, J.; Kcira, D.; Mott, A.; Newman, H. B.; Pena, C.; Rogan, C.; Spiropulu, M.; Timciuc, V.; Wilkinson, R.; Xie, S.; Zhu, R. Y.; Dias, F. A.; Dubinin, M.
Measurements are reported of the WZ and ZZ production cross sections in proton-proton collisions at √s=8 TeV in final states where one Z boson decays to b-tagged jets. The other gauge boson, either W or Z, is detected through its leptonic decay (either W→eν, μν or Z→e^+e^−, μ^+μ−, or νν). The results are based on data corresponding to an integrated luminosity of 18.9 fb^(−1) collected with the CMS detector at the Large Hadron Collider. The measured cross sections, (pp→WZ)=30.7±9.3(stat.)±7.1(syst.)±4.1(th.)±1.0(lum.)pb and σ(pp→ZZ)=6.5±1.7(stat.)±1.0(syst.)±0.9(th.)±0.2(lum.)pb , are consistent with next-to-leading order quantum chromodynamics calculations.

17. Structure of the earth's crust and the spreading of the continents - Gutenberg, Beno
According to the Wegener hypothesis, the continents originally formed a single block. This broke into sections in the Carboniferous, and, during the geologic periods that followed, the continents drifted apart. Wegener, as many others had done before him, originally conceived the idea that the similarity in the coast lines of Europe-Africa and America indicated connection previous to the Carboniferous. It is to his credit, however, that he investigated in detail all the possible consequences of this hypothesis. He considered especially the present-day relative movements of parts of the earth’s crust, and he started investigations of the movement of Greenland relative...

18. Fourier ptychographic microscopy for filtration-based circulating tumor cell enumeration and analysis - Williams, Anthony; Chung, Jaebum; Ou, Xiaoze; Zheng, Guoan; Rawal, Siddharth; Ao, Zheng; Datar, Ram; Yang, Changhuei; Cote, Richard
Circulating tumor cells (CTCs) are recognized as a candidate biomarker with strong prognostic and predictive potential in metastatic disease. Filtration-based enrichment technologies have been used for CTC characterization, and our group has previously developed a membrane microfilter device that demonstrates efficacy in model systems and clinical blood samples. However, uneven filtration surfaces make the use of standard microscopic techniques a difficult task, limiting the performance of automated imaging using commercially available technologies. Here, we report the use of Fourier ptychographic microscopy (FPM) to tackle this challenge. Employing this method, we were able to obtain high-resolution color images, including amplitude and...

19. Regional variations in the structure of the crust in the central United States from P-wave spectra - Kurita, Tuneto
Regional variations in the crustal structure in the central United States have been inferred by the transfer ratio method from an analysis of long-period P waves recorded at SHA, OXF, FLO and MDS, the stations nearly along 89°W longitude. The crustal structure in this region is approximated by a stack of horizontal parallel layers except possibly in the area around FLO, where the structure is rather complicated. The crustal thickness is predominantly controlled by the thick silicic upper crust, whereas the mafic lower crust is about 10 km thick throughout this region. The P-wave velocity of the lower crust is...

20. Shear-wave travel times from SS - Butler, Rhett
The seismic shear phase SS is considered as a tool in the reconnaissance of the Earth. The Hibert transform is empirically verified as a reasonable mimic of the distortion incurred at the internal caustic in the propagation of SS. Travel times are obtained by a waveform correlation technique for 26 well-recorded SHSH waves from the 1968 Borrego Mountain earthquake. Significant variation is found in the travel-time residuals for paths reflected under the Canadian shield. A correlation of the variation with tectonic sub-province is suggested. The data are sufficiently precise to indicate lateral heterogeneity of several percent in the upper mantle...

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