3,329 research outputs found
Subspace estimation and prediction methods for hidden Markov models
Hidden Markov models (HMMs) are probabilistic functions of finite Markov
chains, or, put in other words, state space models with finite state space. In
this paper, we examine subspace estimation methods for HMMs whose output lies a
finite set as well. In particular, we study the geometric structure arising
from the nonminimality of the linear state space representation of HMMs, and
consistency of a subspace algorithm arising from a certain factorization of the
singular value decomposition of the estimated linear prediction matrix. For
this algorithm, we show that the estimates of the transition and emission
probability matrices are consistent up to a similarity transformation, and that
the -step linear predictor computed from the estimated system matrices is
consistent, i.e., converges to the true optimal linear -step predictor.Comment: Published in at http://dx.doi.org/10.1214/09-AOS711 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Nonparametric estimation of mixing densities for discrete distributions
By a mixture density is meant a density of the form
, where
is a family of probability densities and
is a probability measure on . We consider the problem of
identifying the unknown part of this model, the mixing distribution , from
a finite sample of independent observations from . Assuming that the
mixing distribution has a density function, we wish to estimate this density
within appropriate function classes. A general approach is proposed and its
scope of application is investigated in the case of discrete distributions.
Mixtures of power series distributions are more specifically studied. Standard
methods for density estimation, such as kernel estimators, are available in
this context, and it has been shown that these methods are rate optimal or
almost rate optimal in balls of various smoothness spaces. For instance, these
results apply to mixtures of the Poisson distribution parameterized by its
mean. Estimators based on orthogonal polynomial sequences have also been
proposed and shown to achieve similar rates. The general approach of this paper
extends and simplifies such results. For instance, it allows us to prove
asymptotic minimax efficiency over certain smoothness classes of the
above-mentioned polynomial estimator in the Poisson case. We also study
discrete location mixtures, or discrete deconvolution, and mixtures of discrete
uniform distributions.Comment: Published at http://dx.doi.org/10.1214/009053605000000381 in the
Annals of Statistics (http://www.imstat.org/aos/) by the Institute of
Mathematical Statistics (http://www.imstat.org
MEDVINDENS TID Ekologiska Lantbrukarna och jordbrukspolitiken 1985â2000
Under 1980- och 90-talen utmÀrktes jordbrukspolitiken i Sverige av tvÀra kast, först till följd av krav pÄ avreglering och marknadsanpassning, sedan genom medlemskapet i EU. Det bidrog till att sektorns policynÀtverk blev mer öppet Àn under föregÄende Ärtionden. Under samma period gynnades det ekologiska jordbrukets utveckling av det allmÀnna miljömedvetandet och konsumenternas ökande efterfrÄgan. De flesta faktorerna i den politiska möjlighetsstrukturen var dÀrför positiva för Alternativodlarnas Riksförbund/Ekologiska Lantbrukarna.
FrÄn starten 1985 arbetade sig organisationen mÄlmedvetet och med framgÄng in i nÀtverket. Lantbruksmyndigheterna insÄg snart att ARF/Ekologiska Lantbrukarna med sin specialistkompetens kunde tillföra nya vÀrdefulla resurser. De slÀppte dÀrför in organisationens representanter i sina arbetsgrupper, Àven om det inledningsvis mest handlade om mindre betydelsefulla detaljfrÄgor. Efter en viss inledande misstÀnksamhet accepterades nykomlingen av det dominerande LRF, som började fÄ upp ögonen för ekojordbrukets kommersiella potential. I den partipolitiska debatten spelade miljöfrÄgorna i slutet av Ättiotalet en avgörande roll, vilket gjorde att det ekologiska jordbruket uppmÀrksammades av politiker frÄn de flesta partier. OmlÀggningsstödet 1989 kan betraktas som ett genombrott och i fortsÀttningen var sÄvÀl ekologiskt jordbruk som dess ledande intresseorganisation definitivt en kraft att rÀkna med. I mitten av nittiotalet kunde ytterligare framgÄngar skördas.
Först stÀllde sig riksdagen bakom tioprocentsmÄlet och tog ett beslut om permanent ekostöd. Efter EU-intrÀdet infördes nya bidrag i en sÄdan omfattning att alltfler bönder av ekonomiska skÀl övergick till ekologisk produktion. NÀr tioprocentsmÄlet var uppfyllt stÀllde statsmakterna genast in siktet pÄ tjugo procent.
Utvecklingen stötte helt naturligt pĂ„ motstĂ„nd frĂ„n intressen som kunde förlora pĂ„ en omfördelning av resurser frĂ„n det konventionella jordbruket. Det Ă€r trots allt befogat att beskriva den undersökta femtonĂ„rsperioden som en tid av medvind för ARF/Ekologiska Lantbrukarna. Den snabba tillvĂ€xten medförde emellertid en risk för konflikter mellan ideal och verklighet. Ekobönderna var nu mer beroende av bidrag Ă€n tidigare och ekonomiska övervĂ€ganden spelade en större roll för mĂ„nga medlemmar Ă€n i organisationens barndom. Lönsamhetskalkyler kolliderade med ideologin och âpionjĂ€randanâ försvagades nĂ€r rörelsen började institutionaliseras. En annan konsekvens av organisationens ökande inflytande var att ledningen mĂ„ste ta ansvar för politiska beslut som den medverkat till, Ă€ven om en del medlemmar missgynnades. Disciplinering av medlemsopinionen Ă€r en inte sĂ€rskilt behaglig men oundviklig följd av medverkan i en korporativ beslutsprocess.
I takt med det ekologiska jordbrukets tillvĂ€xt har ett inbyggt dilemma gjort sig mer och mer pĂ„mint. Det har blivit allt tydligare att Ekologiska Lantbrukarnas jordbrukspolitiska agerande prĂ€glas av en mĂ„lkonflikt. Dels vill man pĂ„verka hela jordbrukets utveckling i ekologisk riktning, dels fungerar man som intresseorganisation för en avgrĂ€nsad grupp. Det senare syftet gynnas av en klar skiljelinje mellan ekologisk och konventionell produktion och om det konventionella jordbruket blir mer miljövĂ€nligt suddas grĂ€nsen ut. DĂ„ kan det bli svĂ„rare att motivera sĂ„vĂ€l ekostöd som högre priser pĂ„ ekologiska livsmedel. Ekologiska Lantbrukarnas ledning anser dock inte att mĂ„lkonflikten Ă€r nĂ„got större problem. Ăn sĂ„ lĂ€nge Ă€r det nog en riktig bedömning, men i det lĂ„nga loppet kan en försvagad ekologisk identitet visa sig ödesdiger. Den lĂ„ngsiktiga utvĂ€g som organisationens ledning pekar pĂ„ Ă€r att stegvis skĂ€rpa normerna för vad som fĂ„r rĂ€knas som ekologiskt. Utan tvivel finns det en hel del att göra, eftersom dagens ekojordbruk i ett lĂ€ngre tidsperspektiv inte kan betraktas som uthĂ„lligt. Exempelvis har det minst lika hög energiförbrukning som det konventionella jordbruket. Om man kan finna lösningar pĂ„ sĂ„dana utmaningar kan ekojordbruket fortsĂ€tta att vara en spjutspets och dĂ„ kan det Ă€ven fortsĂ€ttningsvis gĂ„ att motivera sĂ€rskilda bidrag och högre priser.
NÀr denna undersökning sÀtter punkt Är 2000 var huvuddragen i jordbrukspolitiken fastlagda för flera Är framÄt, bÄde i Sverige och i EU. Det stod emellertid klart att en ökad miljöanpassning av CAP kommer att tvingas fram, om inte annat sÄ för att ÄterstÀlla konsumenternas förtroende efter BSE-krisen. NÀr den nya CAP-budgeten skall antas 2006 mÄste EU ha kommit fram till nya riktlinjer och diskussionerna kommer att bli intensiva fram till dess. En första etapp Àr den halvtidsöversyn av Agenda 2000 som skall göras 2003. Att CAP i framtiden kommer att innehÄlla mer miljövillkor och satsningar pÄ ekologiskt jordbruk Àr ingen ogrundad gissning. Vid en EU-konferens i Köpenhamn i maj 2001 antogs en deklaration om att EU bör utarbeta en handlingsplan för ekologisk produktion, vilket omgÄende fick stöd av jordbruksministrarna. Vid toppmötet i Göteborg i juni samma Är uttalades att jordbrukspolitiken skall inriktas pÄ uthÄllighet, bland annat genom att frÀmja ekologisk produktion. Kommissionens utkast till halvtidsöversyn, som offentliggjordes i juli 2002, visade sig överraskande radikalt. Franz Fischler föreslÄr att direktstöden trappas ned med tre procent per Är och att dessa medel gÄr till miljöstöd och landsbygdsutveckling. Dessutom vill han lÀgga om hela bidragssystemet. IstÀllet för stöd Ät produktionen skall varje gÄrd fÄ ett samlat inkomststöd pÄ villkor att grundlÀggande miljö- och djurskyddsnormer uppfylls. Med dessa förslag öppnas dörren för Ànnu större förÀndringar lÀngre fram.
I Sverige hade Ekologiska Lantbrukarna mot slutet av 1990-talet stort inflytande pÄ utredningar och beslut i de flesta frÄgor med anknytning till den ekologiska produktionen. I den allmÀnna jordbrukspolitiken var dÀremot organisationens pÄverkan pÄ den svenska linjen fortfarande begrÀnsad. Ett liknande mönster kan iakttas pÄ EU-nivÄ, dÀr synpunkter frÄn IFOAM:s EU-grupp hittills endast beaktats nÀr det gÀllt detaljregler för den ekologiska produktionen. NÀr stora beslut som Agenda 2000 fattats har det varit mÀktigare intressen som avgjort. Kanske kommer företrÀdarna för det ekologiska jordbruket att kunna spela en mer framtrÀdande roll nÀsta gÄng och kanske kommer de dÄ att kunna pÄverka annat Àn detaljfrÄgor
Statistical modeling of warm-spell duration series using hurdle models
Regression models for counts could be applied to the earth sciences, for instance when studying trends of extremes of climatological quantities. Hurdle models are modified count models which can be regarded as mixtures of distributions. In this paper, hurdle models are applied to model the sums of lengths of periods of high temperatures. A modification to the common versions presented in the literature is presented, as left truncation as well as a particular treatment of zeros is needed for the problem. The outcome of the model is compared to those of simpler count models
Environmental effects of carsharing: Results from the moses project
This study shows that car-sharing reduces car mileage by 28-45% among private users, which is quite in line with other studies of car-sharing. Some people increase their driving when joining car- sharing (mainly those who did not own a car before), but the increase is rather small in absolute figures. Some people decrease their driving when joining car-sharing, mainly those who got rid of a car when joining. But all changes put together mean an average decrease with 3000 km per member and year in both Bremen and Belgium. On the other hand the use of public transport is increased by 1100 km per car-sharing member and year. Car-sharing cars are smaller and newer compared to the private cars they replace. Among the total fleet of cars, the share of medium sized cars is reduced by 40%. 65% of abolished cars in Belgium were from 1995 or earlier, which can be compared to the car-sharing fleets average production year of 2002 (these figures are es- timated to be relevant also for Bremen). Due to the above factors, car-sharing is estimated to re- duce CO2 emissions from car transport by 40-50% (among its members), and other pollutants are estimated to decrease even more than 50%. Car-sharing reduces the need for a private car and therefore also reduces the amount of cars in urban areas. In Bremen each car-sharing car replaces 7-10 private cars and in Belgium each car-sharing car replaces 4-6 private cars. This in turn re- duces the need for parking space by 90-135 m2 in Bremen and 45-75 m2 in Belgium for each car- sharing car
Chronic bone marrow failure and transfusion patterns : epidemiological studies of blood transfusions and outcomes in patients with myelodysplastic syndromes
Myelodysplastic syndromes (MDS) encompass a diverse group of clonal hematological
malignancies characterized by dysplasia and ineffective hematopoiesis with an increased risk
of leukemic evolution. It is a disease of the elderly with a median age of nearly 75 years.
Anemia is the most common cytopenia and a majority of the patients have a temporary or
chronic need for red blood cell (RBC) transfusions, either during treatment or at loss of
response to treatment. Recognizing the importance of RBC transfusions, the transfusion
burden is likewise associated with a reduced overall and progression-free survival and with
other unwanted effects, such as alloimmunization and impaired quality of life. This thesis
aimed to expand the knowledge on transfusion patterns primarily in patients with MDS, but
also to investigate transfusion patterns in hematological malignancies overall. Specific goals
were to characterize transfusion patterns, identify clinical and patient-specific parameters
associated with transfusion intensity and to investigate variables that might affect the efficacy
of the RBC transfusion, such as RBC storage time and alloimmunization.
In study I, we presented a nation-wide overview of transfusion patterns in patients diagnosed
with a hematological malignancy of myeloid, lymphoid or plasma cell origin, during the first
two years following diagnosis. Great variations in the transfusion patterns were observed
between hematological diagnoses with regard to transfusion incidence, median number of
transfused units and direct costs. Patients with acute leukemia and MDS received the highest
cumulative number of transfusions and thereby accounted for the highest costs. Conversely,
patients with chronic lymphoid leukemia, Hodgkinâs lymphoma or follicular lymphoma
received the lowest cumulative number of transfusions. The transfusion incidence was
highest immediately after diagnosis in patients with acute leukemia and in patients
undergoing allogeneic stem cell transplantation.
In study II, we aimed to identify clinical and patient-specific parameters associated with
transfusion intensity of RBC and platelet transfusions, in patients with MDS. Independent
predictors of RBC and platelet transfusion intensity were male sex and mutations in genes
encoding histone modulation, signaling and transcriptional regulation. We observed that
transfusion intensity was significantly associated with poor survival.
In study III, we investigated if duration of RBC storage affected the hemoglobin increment
following RBC transfusions in a cohort of MDS patients. A longer duration of RBC storage
was associated with a smaller increment of the hemoglobin level after transfusion, per RBC
unit, compared to units stored less than five days. The estimates proved stable when adjusting
for age and sex and in five different sensitivity analyses.
In study IV, we analyzed risk factors of alloimmunization and potential clinical changes
following alloimmunization, such as transfusion requirements and the post-transfusion
hemoglobin increment, in an MDS cohort. Female sex and a positive direct antiglobulin test
were significantly associated with alloimmunization. Following alloimmunization, we observed an increase of the average transfusion intensity and estimated lower post-transfusion
hemoglobin increments per RBC unit.
In conclusion, characterization of transfusion patterns and identification of variables
associated with transfusion intensity are of great importance and could guide therapeutic
options and optimize transfusion therapy to patients with a chronic bone marrow failure due
to MDS
Surface Wave Testing of Pavements
A novel approach for surface wave testing of pavements is presented. It is a non-destructive testing (NDT) technique that can be used to obtain the thickness and stiffness properties of the different layers in a pavement. With this method structural properties of the pavement can be mapped as a function of time and space, providing a valuable tool in pavement design and management. The technical development is based on a theoretical study of wave propagation in pavement structures and on the reported difficulties experienced with existing methods. A computer based data acquisition system and program for evaluation of layer properties have been developed. From the theoretical study on wave propagation in pavement structures, it is concluded that the nature of wave propagation has been oversimplified in previous studies. Results show that the measurable wave field at the surface of a pavement structure is dominated by leaky quasi-Lamb waves in the first and second layer. The fundamental anti-symmetric mode of vibration is the dominating mode generated in the stiff top layer. This mode drives the complete system and continuity across the boundaries generates higher order modes in the embedded second layer. The interaction of leaky Lamb waves in the first two layers results in large variations in the excitability and the attenuation, so that only the waves corresponding to certain portions of the dispersion curves are measurable at the pavement surface. These portions of dispersion curves (mode branches) are critical for a refined NDT technique for pavements. To resolve the different mode branches it is necessary to record the complete wave field on the pavement surface. In this study the multichannel data acquisition method is replaced by multichannel simulation with one receiver (MSOR). This method uses only one accelerometer-receiver and a light hammer-source, to generate a synthetic receiver array. The recorded data is automatically and objectively transformed to a phase velocity spectrum through the multichannel analysis of surface waves (MASW) processing scheme. The top layer thickness, and stiffness properties are obtained automatically in the field by a Lamb wave analysis of the measured phase velocity spectrum. The inversion of deeper embedded layers is based on the full phase velocity spectrum. The main benefit from the developed inversion procedure is that the raw field data can be automatically processed and inverted without any subjective user input to identify discrete dispersion curves. The viscoelastic properties of the asphalt layer are included to produce the asphalt stiffness as a function of frequency, a mastercurve. In this study the presented NDT technique is applied to pavements and concrete structures. However, generic findings here may also be useful in other fields. Possible applications are; ultrasonic testing of coated materials and sandwich structures, surface wave soil site characterization, and medical applications
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