976 research outputs found
Inert states of spin-S systems
We present a simple but efficient geometrical method for determining the
inert states of spin-S systems. It can be used if the system is described by a
spin vector of a spin-S particle and its energy is invariant in spin rotations
and phase changes. Our method is applicable to an arbitrary S and it is based
on the representation of a pure spin state of a spin-S particle in terms of 2S
points on the surface of a sphere. We use this method to find candidates for
some of the ground states of spinor Bose-Einstein condensates.Comment: 4 pages, 2 figures, minor changes, references added, typos correcte
Explicit expressions for the topological defects of spinor Bose-Einstein condensates
In this paper we first derive a general method which enables one to create
expressions for vortices and monopoles. By using this method we construct
several order-parameters describing the vortices and monopoles of Bose-Einstein
condensates with hyperfine spin F=1 and F=2. We concentrate on defects which
are topologically stable in the absence of an external magnetic field. In
particular we show that in a ferromagnetic condensate there can be a vortex
which does not produce any superfluid flow. We also point out that the
order-parameter space of the cyclic phase of F=2 condensate consists of two
disconnected sets. Finally we examine the effect of an external magnetic field
on the vortices of a ferromagnetic F=1 condensate and discuss the experimental
preparation of a vortex in this system.Comment: 17 pages, partly rewritten to improve clarity, conclusions unchange
Interplanetary shocks lacking type II radio bursts
We report on the radio-emission characteristics of 222 interplanetary (IP)
shocks. A surprisingly large fraction of the IP shocks (~34%) is radio quiet
(i.e., the shocks lacked type II radio bursts). The CMEs associated with the RQ
shocks are generally slow (average speed ~535 km/s) and only ~40% of the CMEs
were halos. The corresponding numbers for CMEs associated with radio loud (RL)
shocks are 1237 km/s and 72%, respectively. The RQ shocks are also accompanied
by lower peak soft X-ray flux. CMEs associated with RQ (RL) shocks are
generally accelerating (decelerating). The kinematics of CMEs associated with
the km type II bursts is similar to those of RQ shocks, except that the former
are slightly more energetic. Comparison of the shock The RQ shocks seem to be
mostly subcritical and quasi-perpendicular. The radio-quietness is predominant
in the rise phase and decreases through the maximum and declining phases of
solar cycle 23. The solar sources of the shock-driving CMEs follow the sunspot
butterfly diagram, consistent with the higher-energy requirement for driving
shocks
Some quantitative data on the role of the ruminant proventriculi in the digestion and absorption of nitrogen-free organic matter
Fourteen cows and five young bulls were fed with hay uniformly during 10 days. After slaughtering, the ingesta of the abomasum were removed and sampled. From the hay, from the contents of the abomasum, and from the feces lignin, N-free organic matter, and N-free non-lignin organic matter were determined. Using the lignin ratio principle, the digestibility of the two N-free fractions was calculated both for the proventriculi and for the whole digestive tract. It appeared that of the total amount of the N-free non-lignin organic matter digested in the whole digestive tract, 76—99 % was digested in the proventriculi. If the results for two of the cows are discarded, the limits in the cows are 85 and 91 %. On the basis of this investigation it can be concluded that in cattle carbohydrates are digested mainly in the proventriculi and their degradation products are absorbed principally from these stomachs
Temporal variations in black carbon concentrations with different time scales in Helsinki during 1996?2005
International audienceVariations in black carbon (BC) concentrations over different timescales, including annual, weekly and diurnal changes, were studied during ten years in Helsinki, Finland. Measurements were made in three campaigns between 1996 and 2005 at an urban area locating two kilometres of the centre of Helsinki. The first campaign took place from November 1996 to June 1997, the second from September 2000 to May 2001 and the third from March 2004 to October 2005. A detailed comparison between the campaigns was only made for winter and spring months when data from all campaigns existed. The effect of traffic and meteorological variables on the measured BC concentrations was studied by means of a multiple regression analysis, where the meteorological data was obtained from a meteorological pre-processing model (MPP-FMI). The BC concentrations showed annual pattern with maxima in fall and late winter due to the weakened mixing and enhanced emissions. Between 1996 and 2005, the campaign median BC concentrations decreased slightly from 1.11 to 1.00 ?g m?3. The lowest campaign median concentration (0.93 ?g m?3) was measured during the second campaign in 2000?2001, when also the lowest traffic rates were measured. The strongest decrease between Campaigns 1 and 3 was observed on weekday daytimes, when also the traffic rates are highest. The variables affecting the measured BC concentrations most were traffic, wind speed and mixing height. On weekdays, traffic had clearly the most important influence before the wind speed and on weekends the effect of wind speed diluted the effect of traffic. The affecting variables and their influence on the BC concentrations were similar in winter and spring. The separate examination of the three campaigns showed that the effect of traffic on the BC concentrations had decreased during the studied years. This reduction was caused by lower emitting vehicles, since between years 1996 and 2005 the traffic rates had increased
Black carbon concentration trends in Helsinki during 1996?2005
International audienceThe black carbon (BC) concentration trends were studied during ten years in Helsinki, Finland. Measurements were made in three campaigns between 1996 and 2005 at an urban area locating two kilometres from the centre of Helsinki. The first campaign was from November 1996 to June 1997, the second from September 2000 to May 2001 and the third from March 2004 to October 2005. In this study, only data from winter and spring months was analysed. The effect of traffic and meteorological variables on the measured BC concentrations was studied by means of a multiple regression analysis, where the meteorological data was obtained from a meteorological pre-processing model (MPP-FMI). During the ten years, the campaign median BC concentrations were found to decrease slightly from 1.11 to 1.00 ?g m?3. The lowest campaign median concentration (0.93 ?g m?3) was measured during the second campaign in 2000?2001, when also the lowest traffic rates were measured. The strongest decrease between campaigns 1 and 3 was observed during weekday daytimes, when the traffic rates are highest. The variables affecting the measured BC concentrations most were traffic, wind speed and mixing height. On weekdays, traffic had clearly the most important influence and on weekends the effect of wind speed diluted the effect of traffic. The affecting variables and their influence on the BC concentration were similar in winter and spring. The separate examination of the three campaigns showed that the effect of traffic on the BC concentrations had decreased during the studied years. This reduction was caused by cleaner emissions from vehicles, since between years 1996 and 2005 the traffic rates had increased. A rough estimate gave that vehicle number-scaled BC mass concentrations have decreased from 0.0028 to 0.0020 ?g m?3 between campaigns 1 and 3
Biogeophysical impacts of peatland forestation on regional climate changes in Finland
Land cover changes can impact the climate by influencing the surface
energy and water balance. Naturally treeless or sparsely treed peatlands were extensively
drained to stimulate forest growth in Finland over the second half
of 20th century. The aim of this study is to investigate the
biogeophysical effects of peatland forestation on regional climate in
Finland. Two sets of 18-year climate simulations were done with the
regional climate model REMO by using land cover data based on
pre-drainage (1920s) and post-drainage (2000s) Finnish national
forest inventories.
In the most intensive peatland forestation area, located in the middle west of Finland, the results show a warming in April of up to 0.43 K in
monthly-averaged daily mean 2 m air temperature, whereas a slight
cooling from May to October of less than 0.1 K in general is found.
Consequently, snow clearance days over that area
are advanced up to 5 days in the mean of 15 years. No clear
signal is found for precipitation. Through analysing the simulated
temperature and energy balance terms, as well as snow depth over
five selected subregions, a positive feedback induced by peatland
forestation is found between decreased surface albedo and increased
surface air temperature in the snow-melting period. Our modelled
results show good qualitative agreements with the observational
data. In general, decreased surface albedo in the snow-melting period and
increased evapotranspiration in the growing period are the most
important biogeophysical aspects induced by peatland forestation
that cause changes in climate. The results from this study can be further integrally analysed with biogeochemical effects of peatland forestation
to provide background information for adapting future forest management to mitigate climate warming effects. Moreover, they
provide insights about the impacts of projected forestation of tundra at high latitudes due to climate change
Evaluation of multivalency as an organization principle for the efficient synthesis of doubly and triply threaded amide rotaxanes
Mono-, di- and trivalent pseudorotaxanes with tetralactam macrocycle hosts and
axles containing diamide binding stations as the guests have been synthesised.
Their threading behaviour was analyzed in detail by NMR experiments and
isothermal titration calorimetry. An X-ray crystal structure of the monovalent
pseudorotaxane confirms the binding motif. Double mutant cycle analysis
provides the effective molarities and insight into the chelate cooperativity
of multivalent binding. While the second binding event in a trivalent
pseudorotaxane exhibits a slightly positive cooperativity, the third binding
is nearly non-cooperative. Nevertheless, the enhanced binding affinities
resulting from the multivalent interaction are the basis for a highly
efficient synthesis of di- and trivalent rotaxanes through stoppering the axle
termini by “click” chemistry. Evidence for the multiply threaded geometry
comes from NMR spectroscopy as well as tandem mass-spectrometric fragmentation
experiments of mass-selected rotaxane ions in the gas phase. Furthermore, the
trivalent rotaxane can be controlled by external stimuli (chloride addition
and removal) which lead to an elevator-type movement of the wheel along the
axle
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