Paramagnetically induced nuclear magnetic resonance relaxation in solutions containing S ≥ 1S⩾1 ions: A molecular-frame theoretical and physical model

The enhancement of nuclear magnetic resonance (NMR) relaxation rates produced by paramagnetic solutes is physically rather different for electron spin S = 1/2S=1/2 paramagnetic species than for S ≥ 1S⩾1 species due to the presence of zero-field splitting interactions in the electron spin Hamiltonians of the latter. When the zfs energy is larger than the electronic Zeeman energy, the electron spin precessional motion is spatially quantized with respect to the molecule-fixed principal axis system (PAS) of the zfs tensor rather than along the external laboratory magnetic field. An analytical theory of the orthorhombic zfs limit has been derived in which the motion of the electron spin variables is described in the zfs-PAS and that of the nuclear spin variables in the laboratory coordinate frame. The resulting theoretical expressions are simple in form and suggest a physically transparent interpretation of the experiment. The NMR relaxation enhancement R1pR1p results from additive contributions, R1x,R1x, R1y,R1y, and R1z,R1z, arising from the molecular-frame Cartesian components of the time-dependent electron spin magnetic moment operator μr(t).μr(t). Each Cartesian component R1rR1r depends on the dipolar power density at the nuclear Larmor frequency that is produced by the corresponding Cartesian component of μr(t).μr(t). The theory displays the dependence of the relaxation enhancement on the variables of molecular structure in a very simple and physically transparent form: R1r∝r−6[1+P2(cos θr)],R1r∝r−6[1+P2(cosθr)], where rr is the interspin distance and cos θrcosθr is the direction cosine of the interspin vector with the rrth principal axis of the zfs tensor. New experimental data are presented for the model S = 1S=1 complex [trans-Ni(II)(acac)2(H2O)2Ni(II)(acac)2(H2O)2] (acac=acetylacetonato)(acac=acetylacetonato) in dioxane solvent. The magnetic field dependence of the proton T1T1 of the axial water ligands has been measured over the range 0.15–1.5 T, the lower end of which corresponds to the zfs limit. The experimental data have been analyzed using the new analytical theory for the zfs-limit regime in conjunction with spin dynamics simulations in the intermediate regime. Dipolar density power plots are presented as graphical devices which clearly exhibit the physical information in the experiment, and which permit a rapid differentiation of the sensitive and insensitive parameters of theory. The data analysis depends strongly on the zfs parameter ∣E∣∣E∣ and on the electron spin relaxation time τS,zτS,z along the zfs-PAS zz-axis, but only very weakly on the other parameters of theory. A fit of the data to theory provided the values ∣E∣ = 1.8±0.1 cm−1∣E∣=1.8±0.1cm−1 and τS,z = 8.0±0.3 ps.τS,z=8.0±0.3ps. © 1997 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71257/2/JCPSA6-107-19-7620-1.pd

Weed Control for Reduced Tillage Systems

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Nuclear magnetic resonance-paramagnetic relaxation enhancements: Influence of spatial quantization of the electron spin when the zero-field splitting energy is larger than the Zeeman energy

Dissolved paramagnetic ions generally provide an efficient mechanism for the relaxation of nuclear spins in solution, a phenomenon called the nuclear magnetic resonance-paramagnetic relaxation enhancement (NMR-PRE). Metal ions with electron spins S ≥ 1S⩾1 exhibit rich NMR relaxation phenomena originating in the properties of the zero-field splitting (zfs) interaction, which vanishes for spin-½12 ions but which is nonzero for S ≥ 1S⩾1 ions in site symmetry lower than cubic. For S ≥ 1S⩾1 ions in the vicinity of the zfs-limit, i.e., at magnetic-field strengths low enough that the zfs energy exceeds the Zeeman energy, the NMR-PRE depends strongly on the detailed structure of the electron spin energy levels as well as on the spatial quantization of the spin motion. It is shown theoretically and experimentally that the NMR-PRE produced by integer spins can be influenced strongly by the small intradoublet zero-field splittings, i.e., the splittings between the components of the non-Kramers doublets, which are produced by noncylindrical components of the crystal field potential. These small splittings produce relatively low-frequency oscillations in the dipolar field associated with 〈〉〈Sẑ〉 (the spin component along the molecule-fixed ẑ axis). These motions decouple the nuclear spin from the electron spin, thereby depressing, in some cases very strongly, the NMR-PRE. The presence of a relatively small Zeeman field, comparable in magnitude to the intradoublet spacing but small compared to the larger interdoublet zfs splittings, causes a major change in the spin wave functions which has profound effects on the motions of the electron spin. When the Zeeman energy exceeds the small zfs splitting, the oscillatory motion of 〈〉〈Sẑ〉 damps out, with the result that the electron spin couples more effectively to the nuclear spin, providing a more efficient NMR relaxation pathway. NMR-PRE data are presented for the S = 1S=1 complex Ni(II)(o-pda)2Cl2Ni(II)(o-pda)2Cl2 (o-pda = ortho-phenylenediamine)(o-pda=ortho-phenylenediamine) which confirm the importance of the splitting of the mS = ±1mS=±1 non-Kramers doublet on the NMR relaxation efficiency. The zfs E-parameter was measured from the NMR data to be ∣E∣ = 0.26 cm−1.∣E∣=0.26cm−1. The S = 2S=2 spin system, Mn(III)Mn(III)-tetraphenylporphyrin sulfonate, exhibits a related phenomenon which arises from the effects of a small zfs splitting, Δϵ±2,Δϵ±2, of the mS = ±2mS=±2 non-Kramers doublet that is caused by a fourfold rotational component of the crystal field potential. The splitting Δϵ±2Δϵ±2 was measured from NMR data to be 0.20 cm−1.0.20cm−1. © 1998 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70721/2/JCPSA6-109-10-4035-1.pd

Risk, balanced skills and entrepreneurship

This paper proposes that risk aversion encourages individuals to invest in balanced skill profiles, making them more likely to become entrepreneurs. By not taking this possible linkage into account, previous research has underestimated the impacts of both risk aversion and balanced skills on the likelihood individuals choose entrepreneurship. Data on Dutch university graduates provide an illustration supporting our contention. We raise the possibility that even risk-averse people might be suited to entrepreneurship; and it may also help explain why prior research has generated somewhat mixed evidence about the effects of risk aversion on selection into entrepreneurship

Nutritional and Metabolic Requirements for the Infection of HeLa Cells by Salmonella enterica Serovar Typhimurium

Salmonella is the causative agent of a spectrum of human and animal diseases ranging from gastroenteritis to typhoid fever. It is a food - and water - borne pathogen and infects via ingestion followed by invasion of intestinal epithelial cells and phagocytic cells. In this study we employed a mutational approach to define the nutrients and metabolic pathways required by Salmonella enterica serovar Typhimurium during infection of a human epithelial cell line (HeLa). We deleted the key glycolytic genes, pfkA and pfkB to show that S. Typhimurium utilizes glycolysis for replication within HeLa cells; however, glycolysis was not absolutely essential for intracellular replication. Using S. Typhimurium strains deleted for genes encoding components of the phosphotransferase system and glucose transport, we show that glucose is a major substrate required for the intracellular replication of S. Typhimurium in HeLa cells. We also deleted genes encoding enzymes involved in the utilization of gluconeogenic substrates and the glyoxylate shunt and show that neither of these pathways were required for intracellular replication of S. Typhimurium within HeLa cells

Gravitational Waves From Known Pulsars: Results From The Initial Detector Era

We present the results of searches for gravitational waves from a large selection of pulsars using data from the most recent science runs (S6, VSR2 and VSR4) of the initial generation of interferometric gravitational wave detectors LIGO (Laser Interferometric Gravitational-wave Observatory) and Virgo. We do not see evidence for gravitational wave emission from any of the targeted sources but produce upper limits on the emission amplitude. We highlight the results from seven young pulsars with large spin-down luminosities. We reach within a factor of five of the canonical spin-down limit for all seven of these, whilst for the Crab and Vela pulsars we further surpass their spin-down limits. We present new or updated limits for 172 other pulsars (including both young and millisecond pulsars). Now that the detectors are undergoing major upgrades, and, for completeness, we bring together all of the most up-to-date results from all pulsars searched for during the operations of the first-generation LIGO, Virgo and GEO600 detectors. This gives a total of 195 pulsars including the most recent results described in this paper.United States National Science FoundationScience and Technology Facilities Council of the United KingdomMax-Planck-SocietyState of Niedersachsen/GermanyAustralian Research CouncilInternational Science Linkages program of the Commonwealth of AustraliaCouncil of Scientific and Industrial Research of IndiaIstituto Nazionale di Fisica Nucleare of ItalySpanish Ministerio de Economia y CompetitividadConselleria d'Economia Hisenda i Innovacio of the Govern de les Illes BalearsNetherlands Organisation for Scientific ResearchPolish Ministry of Science and Higher EducationFOCUS Programme of Foundation for Polish ScienceRoyal SocietyScottish Funding CouncilScottish Universities Physics AllianceNational Aeronautics and Space AdministrationOTKA of HungaryLyon Institute of Origins (LIO)National Research Foundation of KoreaIndustry CanadaProvince of Ontario through the Ministry of Economic Development and InnovationNational Science and Engineering Research Council CanadaCarnegie TrustLeverhulme TrustDavid and Lucile Packard FoundationResearch CorporationAlfred P. Sloan FoundationAstronom

Childhood sarcoidosis: A rare but fascinating disorder

Childhood sarcoidosis is a rare multisystemic granulomatous disorder of unknown etiology. In the pediatric series reported from the southeastern United States, sarcoidosis had a higher incidence among African Americans. Most reported childhood cases have occurred in patients aged 13–15 years. Macrophages bearing an increased expression of major histocompatibility class (MHC) II molecules most likely initiate the inflammatory response of sarcoidosis by presenting an unidentified antigen to CD4+ Th (helper-inducer) lymphocytes. A persistent, poorly degradable antigen driven cell-mediated immune response leads to a cytokine cascade, to granuloma formation, and eventually to fibrosis. Frequently observed immunologic features include depression of cutaneous delayed-type hypersensitivity and a heightened helper T cell type 1 (Th1) immune response at sites of disease. Circulating immune complexes, along with signs of B cell hyperactivity, may also be found. The clinical presentation can vary greatly depending upon the organs involved and age of the patient. Two distinct forms of sarcoidosis exist in children. Older children usually present with a multisystem disease similar to the adult manifestations, with frequent hilar lymphadenopathy and pulmonary infiltrations. Early-onset sarcoidosis is a unique form of the disease characterized by the triad of rash, uveitis, and arthritis in children presenting before four years of age. The diagnosis of sarcoidosis is confirmed by demonstrating a typical noncaseating granuloma on a biopsy specimen. Other granulmatous diseases should be reasonably excluded. The current therapy of choice for sarcoidosis in children with multisystem involvement is oral corticosteroids. Methotrexate given orally in low doses has been effective, safe and steroid sparing in some patients. Alternative immunosuppressive agents, such as azathioprine, cyclophosphamide, chlorambucil, and cyclosporine, have been tried in adult cases of sarcoidosis with questionable efficacy. The high toxicity profile of these agents, including an increased risk of lymphoproliferative disorders and carcinomas, has limited their use to patients with severe disease refractory to other agents. Successful steroid sparing treatment with mycophenolate mofetil was described in an adolescent with renal-limited sarcoidosis complicated by renal failure. Novel treatment strategies for sarcoidosis have been developed including the use of TNF-alpha inhibitors, such as infliximab. The long-term course and prognosis is not well established in childhood sarcoidosis, but it appears to be poorer in early-onset disease

Sequential Immunization Strategies to Elicit HIV-1 bNAbs in Animal Models With a Polyclonal B Cell Repertoire

Background: Immunization regimens that can elicit broadly neutralizing antibodies (bNAbs) in humans would be an effective vaccine against HIV-1. Our previous work showed that an immunization strategy involving a sequence of Env-based germline targeting immunogens that were gradually engineered to resemble the native Env protein, successfully elicited bNAb-like antibodies in a knock-in mouse carrying the inferred germline PGT121/10-1074 antibody. Despite this achievement, immunization protocols that elicit bNAbs in systems with a polyclonal B cell repertoire have not been reported to date. The low frequencies of germline bNAb precursors in polyclonal systems hinder their activation by immunization which therefore requires high affinity immunogens. In addition, competition between different epitope-specific B cells in polyclonal germinal centers may frustrate bNAb development. Methods: Based on our previous results in knock-in mice, we have aimed to optimize sequential immunization strategies to elicit bNAbs in animal models with polyclonal B cell repertoires. Results: The results of immunization experiments in several animal models will be presented