2,668 research outputs found
A three stage model for adsorption of nonionic surfactants
Copyright @ 1993 American Institute of Physics.A three stage model for the adsorption of nonionic surfactants is proposed which makes use of existing theory from studies of random sequential adsorption. The model is simulated and the adsorption curves are found. The theory of random sequential adsorption is used to calculate the coverage exactly at the end of each of the three stages
Deoxyguanosine-resistant Leukemia L1210 Cells: Loss of Specific Deoxyribonecleoside Kinase Activity
A mouse leukemia L1210 cell line was selected for resistance to deoxyguanosine. The deoxyguanosine-resistant cells (dGuo-R) were 126-fold less sensitive to deoxyguanosine than the wild-type cells. The IC50 values for araC and araG were increased, but only 10-12-fold in the dGuo- R cells when compared with the wild-type cells. The dGuo-R cell line showed an increased level of resistance to 2-fluoro-2'-deoxyadenosine and 2-fluoroadenine arabinoside (11-14-fold), but essentially no increase in resistance to deoxyadenosine or adenine arabinoside. Deoxyribonucleoside kinase activity was decreased only slightly (19%) when deoxycytidine was utilized as substrate; when cytosine arabinoside or deoxyguanosine was used as the substrate, the kinase activity in the extracts from the dGuo-R cells was only 10% of the enzyme activity in the extracts from the wild-type cells. The determination of the kinetic parameters, Km and Vmax, indicated that there were marked decreases in the Vmax values for deoxyguanosine and cytosine arabinoside as substrates, but not for deoxycytidine as substrate; the Km values for deoxycytidine and cytosine arabinoside were increased in the extracts from the dGuo-R cells. By use of high-performance liquid chromatography, the kinase activities in the extracts from the wild-type and resistant cells could be resolved. There was the specific loss of kinase activity toward cytosine arabinoside and deoxyguanosine as substrates. These data indicate that the dGuo-R cells have decreased levels of a specific deoxyribonucleoside kinase activity. Originally published Journal of Biological Chemistry, Vol. 268, No. 1, Jan 199
Quantum Simulations on a Quantum Computer
We present a general scheme for performing a simulation of the dynamics of
one quantum system using another. This scheme is used to experimentally
simulate the dynamics of truncated quantum harmonic and anharmonic oscillators
using nuclear magnetic resonance. We believe this to be the first explicit
physical realization of such a simulation.Comment: 4 pages, 2 figures (\documentstyle[prl,aps,epsfig,amscd]{revtex}); to
appear in Phys. Rev. Let
Multi-spin dynamics of the solid-state NMR Free Induction Decay
We present a new experimental investigation of the NMR free induction decay
(FID) in a lattice of spin-1/2 nuclei in a strong Zeeman field. Following a
pi/2 pulse, evolution under the secular dipolar Hamiltonian preserves coherence
number in the Zeeman eigenbasis, but changes the number of correlated spins in
the state. The observed signal is seen to decay as single-spin, single-quantum
coherences evolve into multiple-spin coherences under the action of the dipolar
Hamiltonian. In order to probe the multiple-spin dynamics during the FID, we
measured the growth of coherence orders in a basis other than the usual Zeeman
eigenbasis. This measurement provides the first direct experimental observation
of the growth of coherent multiple-spin correlations during the FID.
Experiments were performed with a cubic lattice of spins (19F in calcium
fluoride) and a linear spin chain (19F in fluorapatite). It is seen that the
geometrical arrangement of the spins plays a significant role in the
development of higher order correlations. The results are discussed in light of
existing theoretical models.Comment: 7 pages, 6 figure
Practical Implementations of Twirl Operations
Twirl operations, which convert impure singlet states into Werner states,
play an important role in many schemes for entanglement purification. In this
paper we describe strategies for implementing twirl operations, with an
emphasis on methods suitable for ensemble quantum information processors such
as nuclear magnetic resonance (NMR) quantum computers. We implement our twirl
operation on a general two-spin mixed state using liquid state NMR techniques,
demonstrating that we can obtain the singlet Werner state with high fidelity.Comment: 6 pages RevTex4 including 2 figures (fig 1 low quality to save space
Seismic Anisotropy and Mantle Dynamics Beneath the Malawi Rift Zone, East Africa
SKS, SKKS, and PKS splitting parameters measured at 34 seismic stations that we deployed in the vicinity of the Cenozoic Malawi Rift Zone (MRZ) of the East African Rift System demonstrate systematic spatial variations with an average splitting time of 1.0 ± 0.3 s. The overall NE-SW fast orientations are consistent with absolute plate motion (APM) models of the African Plate constructed under the assumption of no-net rotation of the global lithosphere and are inconsistent with predicted APM directions from models employing a fixed hot spot reference frame. They also depart considerably from the trend of most of the major tectonic features. These observations, together with the results of anisotropy depth estimation using the spatial coherency of the splitting parameters, suggest a mostly asthenospheric origin of the observed azimuthal anisotropy. The single-layered anisotropy observed at 30 and two-layered anisotropy observed at 4 of the 34 stations can be explained by APM-related simple shear within the rheologically transitional layer between the lithosphere and asthenosphere, as well as by the horizontal deflection of asthenospheric flow along the southern and western edges of a continental block with relatively thick lithosphere revealed by previous seismic tomography and receiver function investigations. This first regional-scale shear wave splitting investigation of the MRZ suggests the absence of rifting-related active mantle upwelling or small-scale mantle convection and supports a passive-rifting process for the MRZ
- …