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Caltech Authors (124,343 recursos)
Repository of works by Caltech published authors.

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Mostrando recursos 1 - 20 de 5,758

1. UC: a language for the connection machine - Bagrodia, R.; Chandy, K. M.; Kwan, E.
n designing parallel languages, the concern for defining a simple virtual machine must be balanced against the need to efficiently map a program on a specific architecture. UC addresses this problem by separating the programming task from efficiency considerations. UC programs are designed using a small set of constructs that include reduction, parallel assignment, and fixed-point computation. The language also provides a map section that may optionally be used by a programmer to specify data mappings for the program. The authors describe the UC constructs and their implementation on the Connection Machine. They also present measurements of the compiler for...

2. Evolution of α-Pinene Oxidation Products in the Presence of Varying Oxidizers: Negative APi-TOF Point of View - Praplan, Arnaud P.; Schobesberger, Siegfried; Junninen, Heikki; Rissanen, Matti P.; Sarnela, Nina; Jokinen, Tujia; Franchin, Alessandro; Duplissy, Jonathan; Sipilä, Mikko; Ehn, Mikael; Petäjä, Tuukka; Worsnop, Douglas R.; Kulmala, Markku
Laboratory experiments conducted in the frame of the CLOUD project at CERN investigated the oxidation of α-pinene oxidation products in a carefully controlled environment and with different oxidation conditions: 1) pure ozonolysis (with the use of an hydroxyl radical (⋅OH) scavenger), 2) ozonolysis without use of a scavenger, and 3) pure ⋅OH oxidation using nitrous acid (HONO) to produce ⋅OH. The anions and negatively charged clusters present in the chamber were analyzed and their chemical composition compared for the different oxidation pathways.

3. Measurements of cluster ions using a nano radial DMA and a particle size magnifier in CLOUD - Franchin, Alessandro; Kangasluoma, Juha; Lehtipalo, Katrianne; Downard, Andrew; Nieminen, Tuomo; Schobesberger, Siegfried; Duplissy, Jonathan; Petäjä, Tuukka; Flagan, Richard; Kulmala, Markku
We built a new instrumental setup for measuring ion distributions in the size range [1.3-6] nm. The implementation of an high transmission inlet increased the total transmission efficiency to more than 6% at 1.47 nm mobility equivalent diameter, allowing the detection of ions at atmospheric concentrations. The size resolution of our measurements is as high as 6. We characterized the instrument in the laboratory and carried out measurements during the CLOUD7 campaign. We compared the results obtained with the Neutral cluster and Air Ion spectrometer finding very good agreement.

4. Constraints on Muon Decay Parameters from Neutrino Mass - Erwin, Rebecca J.
We use experimental limits on the neutrino mass to derive model‐independent upper bounds on various muon decay parameters. We find that the bounds obtained in this way are improved by more than three orders of magnitude over current experimental limits.

5. Aerosol Nucleation and Growth in a Mixture of Sulfuric Acid / Alpha-Pinene Oxidation Products at the CERN CLOUD Chamber - Tröstl, Jasmin; Bianchi, Federico; Kürten, Andreas; Rondo, Linda; Simon, Mario; Sarnela, Nina; Jokinen, Tuija; Heinritzi, Martin; Dommen, Josef; Kirkby, Jasper; Weingartner, Ernest; Baltensperger, Urs
The role of α-pinene in aerosol nucleation and growth was investigated using the CERN CLOUD chamber, a nano scanning mobility particle sizer (nanoSMPS) and several condensation particle counters (CPCs) with different diameter cut-offs. Different oxidation conditions for α-pinene - OH⋅ vs. ozone oxidation - were considered to investigate their contributions to particle nucleation and growth. Results from the latest CERN experiment from fall 2012 (CLOUD 7) are presented.

6. Keeping the History in Historical Seismology: The 1872 Owens Valley, California Earthquake - Hough, Susan E.
The importance of historical earthquakes is being increasingly recognized. Careful investigations of key pre‐instrumental earthquakes can provide critical information and insights for not only seismic hazard assessment but also for earthquake science. In recent years, with the explosive growth in computational sophistication in Earth sciences, researchers have developed increasingly sophisticated methods to analyze macroseismic data quantitatively. These methodological developments can be extremely useful to exploit fully the temporally and spatially rich information source that seismic intensities often represent. For example, the exhaustive and painstaking investigations done by Ambraseys and his colleagues of early Himalayan earthquakes provides information that can be...

7. Cluster Measurements at CLOUD using a High Resolution Ion Mobility Spectrometer - Mass Spectrometer Combination - Adamov, Alexey; Junninen, Heikki; Duplissy, Jonathan; Sipilä, Mikko; Kulmala, Markku
Mass spectrometry is powerful tool for environmental and atmospheric chemistry analysis. Modern mass spectrometers demonstrate low detection limits, high sensitivity, and high resolving power. However, such high performance is not always enough to identify ambient ion clusters due to the clusters braking at the atmospheric pressure-to-vacuum interface of mass spectrometer. This study presents a high resolution ion mobility spectrometer-time-of-flight mass spectrometer (IMS-TOF) in the CLOUD experiment. This combination of orthogonal analytical techniques allows obtaining structural information in addition to mass-to-charge separation.

8. Magnesium Isotopes in Halo Stars - Meléndez, Jorge; Cohen, Judith G.
We have determined Mg isotope ratios in halo field dwarfs and giants in the globular cluster M71 based on high S/N high spectral resolution (R = 10^5) Keck HIRES spectra. Unlike previous claims of an important contribution from intermediate‐mass AGB stars to the Galactic halo, we find that our ^(26)Mg/^(24) Mg ratios can be explained by massive stars.

9. Role of Organics in Particle Nucleation: From the Lab to Global Model - Dommen, Josef; Riccobono, Francesco; Schobesberger, Siegfried; Bianchi, Federico; Scott, Catherine; Ortega, Ismael K.; Rondo, Linda; Breitenlechner, Martin; Junninen, Heikki; Donahue, Neil M.; Kürten, Andreas; Praplan, Arnaud; Weingartner, Ernest; Hansel, Armin; Curtius, Joachim; Kirkby, Jasper; Kulmala, Markku; Carslaw, Kenneth S.; Worsnop, Douglas R.; Baltensperger, Urs
The role of oxidized organic compounds in the process of new particle formation in the atmosphere is poorly known. Here we used the ultraclean and most sophisticated CLOUD chamber to investigate systematically particle formation in the presence of sulfuric acid and oxidized organics. We varied independently the concentrations of both of these components. In addition, nucleation was observed without and in the presence of ionic compounds. From the results a new parameterized description of nucleation was derived for global climate model simulations.

10. Cosmic Infrared Background Experiment (CIBER): A Probe of Extragalactic Background Light from Reionization - Cooray, Asantha; Bock, Jamie; Kawada, Mitsunobu; Keating, Brian; Lee, Dae-Hee; Levenson, Louis; Matsumoto, Toshio; Matsuura, Shuji; Renbarger, Tom; Sullivan, Ian; Tsumura, Kohji; Wada, Takehiko; Zemcov, Michael
The Cosmic Infrared Background ExpeRiment (CIBER) is a rocket‐borne absolute photometry imaging and spectroscopy experiment optimized to detect signatures of first‐light galaxies present during reionization in the unresolved IR background. CIBER‐I consists of a wide‐field two‐color camera for fluctuation measurements, a low‐resolution absolute spectrometer for EBL measurements, and a narrow‐band imaging spectrometer to measure and correct scattered emission from the foreground zodiacal cloud. CIBER‐I was successfully flown on February 25th, 2009 and is expected to be flown three more times over the next two years at six month intervals. CIBER‐II is a wide‐field 30 cm imager operating in 4 bands...

11. Molecular Steps of Neutral Sulfuric Acid and Dimethylamine Nucleation in CLOUD - Jokinen, Tuija; Sarnela, Nina; Sipilä, Mikko; Junninen, Heikki; Lehtipalo, Katrianne; Duplissy, Jonathan
We have run a set of experiments in the CLOUD chamber at CERN, Switzerland, studying the effect of dimethylamine (DMA) on sulfuric acid (SA)-water nucleation using a nitrate based Chemical Ionization Atmospheric Pressure ionization Time-Of-Flight Mass Spectrometer (CI-APi-TOF). Experiment was designed to produce neutral high m/z SA-DMA clusters in close to atmospherically relevant conditions to be detected and characterized by the CI-APi-TOF. We aimed in filling up the gap in measurement techniques from molecular level up to climatically relevant aerosol particles and thus improve our understanding of the role of sulfuric acid and DMA in atmospheric nucleation.

12. Nucleation of H_2SO_4 and oxidized organics in CLOUD experiment - Sipilä, Mikko; Sarnela, Nina; Jokinen, Tuija; Nieminen, Tuomo; Almeida, Joao; Tröstl, Jasmin; Lehtipalo, Katrianne; Duplissy, Jonathan; Junninen, Heikki
The research of atmospheric new particle formation has proceeded lately as the role of sulphuric acid has been established. Still, the roles of other atmospheric compounds in nucleation remain largely unclear. To clarify the first steps of atmospheric new particle formation extensive nucleation experiments were performed in CLOUD chamber in 2012. Especially the role of oxidations products of α-pinene was studied in detail. The experiments provided new information about the part of oxidized organics in nucleation.

13. Charged and Neutral Binary Nucleation of Sulfuric Acid in Free Troposphere Conditions - Duplissy, Jonathan; Merikanto, Joonas; Sellegri, Karine; Rose, Clemence; Asmi, Eija; Freney, Evelyn; Juninen, Heikki; Sipilä, Mikko; Vehkamaki, Hanna; Kulmala, Markku
We present a data set of binary nucleation of sulfuric acid and water, measured in the CLOUD chamber at CERN during the CLOUD3 and CLOUD5 campaigns. Four parameters have been varied to cover neutral and ion-induced binary nucleation processes: Sulfuric acid concentration (1e5 to 1e8 molecules per cm^(−3)), relative humidity (10% to 80%), temperature (208-293K) and ion concentration (0-4000 ions per cm^(−3)). In addition, classical nucleation theory implemented with hydrates and ion induced nucleation is compared with the data set. Our model and data are also compared with nucleation rates measured at Puy de Dome in the tropopause.

14. Measuring Composition & Growth of Ion Clusters of Sulfuric Acid, Ammonia, Amines & Oxidized Organics as First Steps of Nucleation in the CLOUD Experiment - Schobesberger, Siegfried; Praplan, Arnaud P.; Junninen, Heikki; Bianchi, Federico; Lönn, Gustaf; Ehn, Mikael; Lehtipalo, Katrianne; Dommen, Josef; Ehrhart, Sebastian; Franchin, Alessandro; Ortega, Ismael K.; Riccobono, Francesco; Duplissy, Jonathan; Rissanen, Matti P.; Sipilä, Mikko; Petäjä, Tuukka; Kulmala, Markku; Donahue, Neil M.; Worsnop, Douglas R.
The mechanisms behind the nucleation of vapors forming new particles in the atmosphere had been proven difficult to establish. One main aim of the CLOUD experiment was to explore in detail these first steps of atmospheric new particle formation by performing extremely well controlled laboratory experiments. We examined nucleation and growth in the presence of different mixtures of vapors, including sulfuric acid, ammonia, dimethylamine, and oxidation products of pinanediol or α-pinene. Among the employed state-of-the-art instrumentation, a high-resolution mass spectrometer that directly sampled negatively charged ions and clusters proved particularly useful. We were able to resolve most of the chemical...

15. How Do Amines Affect the Growth of Recently Formed Aerosol Particles - Lehtipalo, Katrianne; Schobesberger, Siegfried; Sipilä, Mikko; Jokinen, Tuija; Sarnela, Nina; Franchin, Alessandro; Nieminen, Tuomo; Riccobono, Francesco; Duplissy, Jonathan; Riipinen, Ilona; Kulmala, Markku; Worsnop, Douglas R.
Growth rates of recently born nanometer-scale particles were measured during the CLOUD experiments at CERN. Combining the data from several recently developed measurement techniques allowed us to follow the growth of the particles starting from molecules to molecular clusters and finally to climatically relevant particles. We studied the binary system with sulphuric acid and water, and the ternary systems with ammonia or dimethylamine added to the chamber, both in purely neutral situation, and with ionization from cosmic rays or the CERN particle beam.

16. The CLOUD data acquisition system and online derivation of nucleation rates - Dias, A.; Almeida, J.; Amorim, A.; David, A.; Tomé, A.
The CLOUD data acquisition, online data analysis and control system, address the challenges of online monitoring, control and data plotting, while providing a centralized data repository with unified tools for data access and visualization. The system was optimized for rapid instrument integration and flexible data format processing. It was built upon open architecture components including a computing cluster monitoring and an open database management system. The different approaches for parameter computation available in the CLOUD central data acquisition system are explained.

17. A Double Inversion: Size and Time Resolved Growth Rates for Aerosol Particles in the CERN CLOUD Experiment - Williamson, C.; Curtius, J.; Kürten, A.; Almeida, J.; Ehrhart, S.; Wimmer, D.; Lehtipalo, K.; Tröstl, J.
An integrated analysis of multiple instruments measuring concentrations of aerosol particles in the CLOUD (Cosmics Leaving OUtdoor Droplets) chamber at CERN obtains size and time dependent growth rates. A matrix inversion is performed twice: first to get size distributions from measured concentrations using instrument transfer functions; secondly to get growth rates from size distributions using the aerosol general dynamic equation (GDE).

18. Measurement of neutral sulfuric acid-dimethylamine clusters using CI-APi-TOF-MS - Simon, Mario; Kürten, Andreas; Jokinen, Tuija; Sarnela, Nina; Sipilä, Mikko; Rondo, Linda; Ehrhart, Sebastian; Junninen, Heikki; Hutterli, Manuel; Kirkby, Jasper; Worsnop, Douglas R.; Curtius, Joachim
Recent studies suggest that dimethylamine could be a key ternary species in the formation and early growth of atmospheric aerosol particles. We report on nucleation studies for the ternary system of sulfuric acid, water and dimethylamine which have been performed at the CERN CLOUD chamber. These studies were conducted at atmospherically relevant concentrations of sulfuric acid and dimethylamine at 278 K and 38% RH. Two newly developed Chemical Ionization-Atmospheric Pressure interface-Time of Flight-Mass Spectrometers (CIAPi-TOF-MS) were used to measure the time-resolved concentration of neutral clusters containing sulfuric acid and dimethylamine. Results from other instrumental techniques are included in the analysis...

19. Submillimeter, Far-Infrared Spectroscopy of the Interstellar Medium - Phillips, T. G.
Spectroscopic studies of interstellar clouds can now be made in the submillimeter and far-infrared bands, essentially free from the absorbing effects of the Earth's atmosphere, by means of the NASA Kuiper Airborne Observatory. Also large telescopes for the submillimeter are now under construction on mountain tops. Both high and intermediate resolution spectroscopic techniques have been successfully employed in the detection of many new molecular and atomic lines including rotational transitions of hydrides such as OH , H_20, NH_3 , and HCl; high J rotational transitions of CO; and the ground state fine structure transitions of atomic carbon, oxygen, singly ionized carbon and doubly ionized oxygen and nitrogen. In addition, heavy...

20. Caltech SIS Receivers - Woody, David P.
This paper describes the superconductor-insulator-superconductor (SIS) receivers which are being used in the Owens Valley Radio Observatory Millimeter Interferometer. These receivers operate over the frequency range from 85 to 115 GHz using a simple circular waveguide mixer block design and have achieved double sideband noise temperatures as low as 70 K. They have been in use since 1981 and have proven to be reliable and easy to operate.

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