435 research outputs found
Photo Lewis acid generators: photorelease of B(C6F5)3 and applications to catalysis
A series of molecules capable of releasing of the strong organometallic Lewis acid B(C6F5)3 upon
exposure to 254 nm light have been developed. These photo Lewis acid generators (PhLAGs) can now
serve as photoinitiators for several important B(C6F5)3-catalyzed reactions. Herein is described the synthesis
of the triphenylsulfonium and diphenyliodonium salts of carbamato- and hydridoborates, their
establishment as PhLAGs, and studies aimed at defining the mechanism of borane release. Factors
affecting these photolytic reactions and the application of this concept to photoinduced hydrosilylation
reactions and construction of siloxane scaffolds are also discusse
Photo Lewis acid generators: photorelease of B(C6F5)3 and applications to catalysis
A series of molecules capable of releasing of the strong organometallic Lewis acid B(C6F5)3 upon
exposure to 254 nm light have been developed. These photo Lewis acid generators (PhLAGs) can now
serve as photoinitiators for several important B(C6F5)3-catalyzed reactions. Herein is described the synthesis
of the triphenylsulfonium and diphenyliodonium salts of carbamato- and hydridoborates, their
establishment as PhLAGs, and studies aimed at defining the mechanism of borane release. Factors
affecting these photolytic reactions and the application of this concept to photoinduced hydrosilylation
reactions and construction of siloxane scaffolds are also discusse
The Substructure Hierarchy in Dark Matter Haloes
We present a new algorithm for identifying the substructure within simulated
dark matter haloes. The method is an extension of that proposed by Tormen et
al. (2004) and Giocoli et al. (2008a), which identifies a subhalo as a group of
self-bound particles that prior to being accreted by the main progenitor of the
host halo belonged to one and the same progenitor halo (hereafter satellite).
However, this definition does not account for the fact that these satellite
haloes themselves may also have substructure, which thus gives rise to
sub-subhaloes, etc. Our new algorithm identifies substructures at all levels of
this hierarchy, and we use it to determine the mass function of all
substructure (counting sub-haloes, sub-subhaloes, etc.). On average, haloes
which formed more recently tend to have a larger mass fraction in substructure
and to be less concentrated than average haloes of the same mass. We provide
quantitative fits to these correlations. Even though our algorithm is very
different from that of Gao et al. (2004), we too find that the subhalo mass
function per unit mass at redshift z = 0 is universal. This universality
extends to any redshift only if one accounts for the fact that host haloes of a
given mass are less concentrated at higher redshifts, and concentration and
substructure abundance are anti-correlated. This universality allows a simple
parametrization of the subhalo mass function integrated over all host halo
masses, at any given time. We provide analytic fits to this function which
should be useful in halo model analyses which equate galaxies with halo
substructure when interpreting clustering in large sky surveys. Finally, we
discuss systematic differences in the subhalo mass function that arise from
different definitions of (host) halo mass.Comment: 18 pages, 24 figures, accepted for publication on MNRA
The correlation of RNase A enzymatic activity with the changes in the distance between Nepsilon2-His12 and N delta1-His119 upon addition of stabilizing and destabilizing salts.
The effect of stabilizing and destabilizing salts on the catalytic behavior of ribonuclease A (RNase A) was investigated at pH 7.5 and 25 degrees C, using spectrophotometric, viscometric and molecular dynamic methods. The changes in the distance between N(epsilon2) of His(12) and N(delta1) of His(119) at the catalytic center of RNase A upon the addition of sodium sulfate, sodium hydrogen sulfate and sodium thiocyanate were evaluated by molecular dynamic methods. The compactness and expansion in terms of Stokes radius of RNase A upon the addition of sulfate ions as kosmotropic salts, and thiocyanate ion as a chaotropic salt, were estimated by viscometric measurements. Enzyme activity was measured using cytidine 2', 3'-cyclic monophosphate as a substrate. The results from the measurements of distances between N(epsilon2) of His(12) and N(delta1) of His(119) and Stokes radius suggest (i) that the presence of sulfate ions decreases the distance between the catalytic His residues and increases the globular compactness, and (ii) that there is an expansion of the enzyme surface as well as elongation of the catalytic center in the presence of thiocyanate ion. These findings are in agreement with activity measurements
280 GHz Focal Plane Unit Design and Characterization for the SPIDER-2 Suborbital Polarimeter
We describe the construction and characterization of the 280 GHz bolometric
focal plane units (FPUs) to be deployed on the second flight of the
balloon-borne SPIDER instrument. These FPUs are vital to SPIDER's primary
science goal of detecting or placing an upper limit on the amplitude of the
primordial gravitational wave signature in the cosmic microwave background
(CMB) by constraining the B-mode contamination in the CMB from Galactic dust
emission. Each 280 GHz focal plane contains a 16 x 16 grid of corrugated
silicon feedhorns coupled to an array of aluminum-manganese transition-edge
sensor (TES) bolometers fabricated on 150 mm diameter substrates. In total, the
three 280 GHz FPUs contain 1,530 polarization sensitive bolometers (765 spatial
pixels) optimized for the low loading environment in flight and read out by
time-division SQUID multiplexing. In this paper we describe the mechanical,
thermal, and magnetic shielding architecture of the focal planes and present
cryogenic measurements which characterize yield and the uniformity of several
bolometer parameters. The assembled FPUs have high yields, with one array as
high as 95% including defects from wiring and readout. We demonstrate high
uniformity in device parameters, finding the median saturation power for each
TES array to be ~3 pW at 300 mK with a less than 6% variation across each array
at one standard deviation. These focal planes will be deployed alongside the 95
and 150 GHz telescopes in the SPIDER-2 instrument, slated to fly from McMurdo
Station in Antarctica in December 2018
Peningkatan Prestasi Belajar CAD Mahasiswa Teknik Otomotif Non-Reguler FT UNY melalui Pembuatan “Pohon Kata” Perintah dalam Program AutoCAD
Penelitian ini bertujuan meningkatkan prestasi belajar mata kuliah Computer Aided Design (CAD) mahasiswa prodi Teknik Otomotif Non-Reguler yang dinyatakan dalam bentuk rerata nilai akhir semester yang berasal dari komponen nilai tugas harian, nilai ujian tengah semester dan nilai ujian akhir semester. Penelitian quasi-eksperimen ini terdiri dari tahapan penelitian diawali dengan penyusunan materi pembelajaran sejumlah pokok bahasan tertentu dalam satu job sheet (lembar kerja), dilanjutkan dengan pembuatan bantuan “Pohon Kata” perintah dalam Auto CAD kepada kelas eksperimen yang ditentukan secara random dari dua kelas peserta kuliah Auto CAD pada Semester Genap 2008/2009. Kedua kelas diamati prestasinya, baik kecepatan penyelesaiannya maupun kualitas kebenaran gambarnya. Prestasi belajar kedua kelas juga diukur melalui pemberian ujian tengah semester dan ujian akhir semester. Setelah data prestasi kedua kelas terkumpul dilanjutkan dengan analisis statistik melalui uji beda (t-test) setelah sebelumnya dilakukan uji persyaratan analisis yang ternyata dapat dipenuhi. Hasil penelitian ini disimpulkan bahwa: prestasi belajar CAD mahasiswa pada kelas yang diberi perlakuan strategi pembelajaran menggunakan “Pohon Kata” perintah dalam Program Auto CAD lebih baik dibanding prestasi belajar CAD mahasiswa pada kelas yang tidak diberi perlakuan (75,41>70,89), dengan demikian pembelajaran CAD menggunakan media “Pohon Kata” perintah dalam Program Auto CAD dapat meningkatkan prestasi belajar mahasiswa Teknik Otomotif Program Non-Reguler
Cosmic microwave background constraints on the duration and timing of reionization from the South Pole Telescope
The epoch of reionization is a milestone of cosmological structure formation,
marking the birth of the first objects massive enough to yield large numbers of
ionizing photons. The mechanism and timescale of reionization remain largely
unknown. Measurements of the CMB Doppler effect from ionizing bubbles embedded
in large-scale velocity streams (the patchy kinetic Sunyaev-Zel'dovich effect)
can constrain the duration of reionization. When combined with large-scale CMB
polarization measurements, the evolution of the ionized fraction can be
inferred. Using new multi-frequency data from the South Pole Telescope (SPT),
we show that the ionized fraction evolved relatively rapidly. For our basic
foreground model, we find the kinetic Sunyaev-Zel'dovich power sourced by
reionization at l=3000 to be <= 2.1 micro K^2 at 95% CL. Using reionization
simulations, we translate this to a limit on the duration of reionization of
Delta z <= 4.4 (95% CL). We find that this constraint depends on assumptions
about the angular correlation between the thermal Sunyaev-Zel'dovich power and
the cosmic infrared background (CIB). Introducing the degree of correlation as
a free parameter, we find that the limits on kSZ power weaken to <= 4.9 micro
K^2, implying Delta z <= 7.9 (95% CL). We combine the SPT constraint on the
duration of reionization with the WMAP7 measurement of the integrated optical
depth to probe the cosmic ionization history. We find that reionization ended
with 95% CL at z > 7.2 under the assumption of no tSZ-CIB correlation, and
z>5.8 when correlations are allowed. Improved constraints from the full SPT
data set in conjunction with upcoming Herschel and Planck data should detect
extended reionization at >95% CL provided Delta z >= 4. (abbreviated)Comment: 16 pages, 13 figures, version accepted by ApJ, improved forecast of
Herschel-SPT reionization constraint
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