349 research outputs found
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Jordbearbetning Àr en effektiv kontrollmetod mot perenna ogrÀs, sÄsom kvickrot (Elymus repens L.), delvis pÄ grund av att bearbetningen sönderdelar ogrÀsens underjordiska lagringsorgan (rhizom).
Jordbearbetning ökar dock risken för nÀringslÀckage, och det Àr svÄrt att kombinera jordbearbetning med en vÀxande gröda. I denna studie anvÀnde vi oss av en prototyp med vertikala diskar för att fragmentera kvickrotens rhizomer med minimal störning av jord och gröda. MÄlet var att utveckla en metod för kvickrotskontroll i grÀs-klövergrödor med en kombination av rhizomfragmentering och putsning. Experimenten utfördes 2014 och 2015 i Uppsala, med rhizomfragmentering utförd innan sÄdd (TRF), i den vÀxande grödan (SRF) eller bÄde och (TRF + SRF). Rhizomfragmenteringen kombinerades med upprepad putsning och tre vallgrödor (vitklöver, italienskt rajgrÀs eller en blandning av bÄda) samt kontroll.
Resultaten visar att i grÀs-klövergrödan minskade rhizomfragmenteringen vikten av kvickrotsrhizom, ökade mÀngden italienskt rajgrÀs och det fanns en tendens till ökad mÀngd vitklöver.
TRF och SRF hade liknande effekt pÄ kvickrotsrhizomvikten, ca 40 % minskning jÀmfört med kontrollen, men SRF ökade mÀngden italienskt rajgrÀs mer Àn TRF. TRF + SRF hade större effekt Àn en enda fragmentering och reducerade kvickrotsrhizomvikten med 55 % jÀmfört med kontrollen, medan skottvikten av italienskt rajgrÀs tripplades. Upprepad putsning reducerade kvickrotsrhizomvikten med ca 75 % och nÀr putsning kombinerades med rhizomfragmentering var det en tendens till Ànnu större minskning, ca 80 % i genomsnitt. VÄr slutsats Àr att rhizomfragmentering med vertikala diskar kan anvÀndas bÄde innan sÄdd och i den vÀxande grödan för att förbÀttra kontrollen av kvickrot i en grÀs-klövergröda.
The work of this paper is related to Task 1 in work package 2 of the FertilCrop Project - the control of weeds in reduced tillage systems.
The conference was directed towards researchers and stakeholders in forage crop production in the Scandinavian countries (In Swedish). There were about 300 participants, researchers, advisors, industry, officials and farmers
Crack Front Waves and the dynamics of a rapidly moving crack
Crack front waves are localized waves that propagate along the leading edge
of a crack. They are generated by the interaction of a crack with a localized
material inhomogeneity. We show that front waves are nonlinear entities that
transport energy, generate surface structure and lead to localized velocity
fluctuations. Their existence locally imparts inertia, which is not
incorporated in current theories of fracture, to initially "massless" cracks.
This, coupled to crack instabilities, yields both inhomogeneity and scaling
behavior within fracture surface structure.Comment: Embedded Latex file including 4 figure
Spin-3/2 random quantum antiferromagnetic chains
We use a modified perturbative renormalization group approach to study the
random quantum antiferromagnetic spin-3/2 chain. We find that in the case of
rectangular distributions there is a quantum Griffiths phase and we obtain the
dynamical critical exponent as a function of disorder. Only in the case of
extreme disorder, characterized by a power law distribution of exchange
couplings, we find evidence that a random singlet phase could be reached. We
discuss the differences between our results and those obtained by other
approaches.Comment: 4 page
Disorder Induced Phases in Higher Spin Antiferromagnetic Heisenberg Chains
Extensive DMRG calculations for spin S=1/2 and S=3/2 disordered
antiferromagnetic Heisenberg chains show a rather distinct behavior in the two
cases. While at sufficiently strong disorder both systems are in a random
singlet phase, we show that weak disorder is an irrelevant perturbation for the
S=3/2 chain, contrary to what expected from a naive application of the Harris
criterion. The observed irrelevance is attributed to the presence of a new
correlation length due to enhanced end-to-end correlations. This phenomenon is
expected to occur for all half-integer S > 1/2 chains. A possible phase diagram
of the chain for generic S is also discussed.Comment: 6 Pages and 6 figures. Final version as publishe
Mott Transition and Spin Structures of Spin-1 Bosons in Two-Dimensional Optical Lattice at Unit Filling
We study the ground state properties of spin-1 bosons in a two-dimensional
optical lattice, by applying a variational Monte Carlo method to the S=1
Bose-Hubbard model on a square lattice at unit filling. A doublon-holon binding
factor introduced in the trial state provides a noticeable improvement in the
variational energy over the conventional Gutzwiller wave function and allows us
to deal effectively with the inter-site correlations of particle densities and
spins. We systematically show how spin-dependent interactions modify the
superfluid-Mott insulator transitions in the S=1 Bose-Hubbard model due to the
interplay between the density and spin fluctuations of bosons. Furthermore,
regarding the magnetic phases in the Mott region, the calculated spin structure
factor elucidates the emergence of nematic and ferromagnetic spin orders for
antiferromagnetic () and ferromagnetic () couplings,
respectively.Comment: 5 pages, 5 figures, to appear in Journal of the Physical Society of
Japa
Variational Monte Carlo analysis of the Hubbard model with a confining potential: one-dimensional fermionic optical lattice systems
We investigate the one-dimensional Hubbard model with a confining potential,
which may describe cold fermionic atoms trapped in an optical lattice.
Combining the variational Monte Carlo simulations with the new stochastic
reconfiguration scheme proposed by Sorella, we present an efficient method to
systematically treat the ground state properties of the confined system with a
site-dependent potential. By taking into account intersite correlations as well
as site-dependent on-site correlations, we are able to describe the coexistence
of the metallic and Mott insulating regions, which is consistent with other
numerical results. Several possible improvements of the trial states are also
addressed.Comment: 7 pages, 15 figures; removed unnecessary graphs (p.8-p.32 in the old
version are removed
Mortality following development of breast cancer while using oestrogen or oestrogen plus progestin: a computer record-linkage study
The literature on the relationship between breast cancer mortality and postmenopausal oestrogen and combined oestrogen/progestin therapy is seemingly contradictory. This study explored survival after exposure to oestrogen or oestrogen plus progestin at or in the year prior to breast cancer diagnosis. Information on patients first diagnosed with invasive breast cancer between 1993 and 1998 was linked with outpatient pharmacy data from 1992 to 2000. Patients were classified according to use of oestrogen alone or oestrogen plus progestin at or in the year prior to diagnosis. Compared to nonusers, and adjusting for age at diagnosis, race/ethnicity, tumour size and grade, oestrogen receptor status, surgery status, and chemotherapy and hormone therapy for breast cancer treatment, oestrogen plus progestin users had lower all-cause mortality (stage I hazard ratio (HR)=0.69, 95% confidence interval (CI)=0.48â0.99; stage II HR=0.53, 95% CI=0.39â0.72) and breast cancer mortality (stage I HR=0.52, 95% CI=0.26â1.04; stage II HR=0.69, 95% CI=0.48â0.98). Oestrogen users experienced little or no survival benefit for all-cause mortality (stage I HR=1.04, 95% CI=0.77â1.42; stage II HR=0.86, 95% CI=0.65â1.14) or breast cancer mortality (stage I HR=1.23, 95% CI 0.72â2.10; stage II HR=1.01, 95% CI 0.72â1.41). Our findings suggest, relative to nonusers, a lower risk of death from all causes and from breast cancer in patients who were diagnosed with breast cancer while exposed to oestrogen plus progestin, but not in patients exposed to oestrogen only
Effects of work ability and health promoting interventions for women with musculoskeletal symptoms: A 9-month prospective study
<p>Abstract</p> <p>Background</p> <p>Women working in the public human service sector in 'overstrained' situations run the risk of musculoskeletal symptoms and long-term sick leave. In order to maintain the level of health and work ability and strengthen the potential resources for health, it is important that employees gain greater control over decisions and actions affecting their health â a process associated with the concept of self-efficacy. The aim of this study was to describe the effects of a self-efficacy intervention and an ergonomic education intervention for women with musculoskeletal symptoms, employed in the public sector.</p> <p>Methods</p> <p>The design of the study was a 9-month prospective study describing the effects of two interventions, a comprehensive self-efficacy intervention (<it>n </it>= 21) and an ergonomic education intervention (<it>n </it>= 21). Data were obtained by a self-report questionnaire on health- and work ability-related factors at baseline, and at ten weeks and nine months follow-up. Within-group differences over time were analysed.</p> <p>Results</p> <p>Over the time period studied there were small magnitudes of improvements within each group. Within the self-efficacy intervention group positive effects in perceived work ability were shown. The ergonomic education group showed increased positive beliefs about future work ability and a more frequent use of pain coping strategies.</p> <p>Conclusion</p> <p>Both interventions showed positive effects on women with musculoskeletal symptoms, but in different ways. Future research in this area should tailor interventions to participants' motivation and readiness to change.</p
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