89 research outputs found
Extending the reach of uncertainty quantification in nuclear theory
The theory of the strong interactionâquantum chromodynamics (QCD)âis unsuited to practical calculations of nuclear observables and approximate models for nuclear interaction potentials are required. In contrast to phenomenological models, chiral effective field theories (ÏEFTs) of QCD grant a handle on the theoretical uncertainty arising from the truncation of the chiral expansion. Uncertainties in ÏEFT are preferably quantified using Bayesian inference, but quantifying reliable posterior predictive distributions for nuclear observables presents several challenges. First, ÏEFT is parametrized by unknown low-energy constants (LECs) whose values must be inferred from low-energy data of nuclear structure and reaction observables. There are 31 LECs at fourth order in Weinberg power counting, leading to a high-dimensional inference problem which I approach by developing an advanced sampling protocol using Hamiltonian Monte Carlo (HMC). This allows me to quantify LEC posteriors up to and including fourth chiral order. Second, the ÏEFT truncation error is correlated across independent variables such as scattering energies and angles; I model correlations using a Gaussian process. Third, the computational cost of computing few- and many-nucleon observables typically precludes their direct use in Bayesian parameter estimation as each observable must be computed in excess of 100,000 times during HMC sampling. The one exception is nucleon-nucleon scattering observables, but even these incur a substantial computational cost in the present applications. I sidestep such issues using eigenvector-continuation emulators, which accurately mimic exact calculations while dramatically reducing the computational cost. Equipped with Bayesian posteriors for the LECs, and a model for the truncation error, I explore the predictive ability of ÏEFT, presenting the results as the probability distributions they always were
Efficient sampling of Bayesian posteriors and predictive distributions in ÏEFT
In this thesis I employ Bayesian statistics to quantify parametric and epistemic uncertainties in chiral effective field theories (ÏEFT) and propagate these forward to predictions of observables in low-energy nuclear physics. Two primary sources of uncertainty---experimental errors and the theoretical error induced by the truncation of the EFT at up to next-to-next-to-leading-order---are modelled and accounted for in the posterior distributions of the unknown low-energy constants (LECs) that govern interaction strengths in ÏEFT. These posteriors are computationally challenging to extract and I therefore introduce an advanced Markov chain Monte Carlo (MCMC) algorithm, known as Hamiltonian Monte Carlo, and investigate its performance. I compare its sampling efficiency to standard MCMC algorithms and find reductions in computation time by factors around 3-6 in the present work. I exploit the extracted posteriors to produce predictive distributions for neutron-proton and proton-proton scattering cross sections below and above the pion production threshold and check the consistency of the model predictions against empirical data and higher-order point estimates. I find that the predictive distributions provide reliable credibility intervals as long as the size of the truncation error is estimated from expansion coefficients at next-to-leading-order and above. The LEC posteriors are also central to uncertainty quantification in few- and manybody systems, and as part of a larger collaboration I explore constraints on three-nucleon forces imposed by light-nuclei observables
Research on Bias in Mediation: Policy Implications
One of the most important and disputed questions within the field of international mediation concerns the issue of bias. The question of bias cuts to the core of what mediation is and the ways in which mediators can help the parties reach peace. Focusing on research on the role of neutrality and bias in international peace diplomacy in civil wars, this article draws out the policy implications of my own empirically-based work on the role of bias in the mediation of internal armed conflicts. This article suggests that neutrality should not be part of the definition of mediators, and that instead type and degree of bias should be treated as independent variables. In fact, my research has shown that biased mediators, under some conditions, outperform neutral mediators, and also importantly, that it matters in civil wars to which side the mediator is biased: for the government or for the rebel-side. This does not imply that neutral mediators have no role to play in peacemaking processes around the globe: this article discusses explicitly the implications of my research on how neutral mediators should engage themselves in order to bring about peace in civil wars. The article also discusses the notion of âinsider-partialâ, that is, third party actors within the conflict societies and it suggested that it is important to tap these domestic resources for peace
Research on Bias in Mediation: Policy Implications
One of the most important and disputed questions within the field of international mediation concerns the issue of bias. The question of bias cuts to the core of what mediation is and the ways in which mediators can help the parties reach peace. Focusing on research on the role of neutrality and bias in international peace diplomacy in civil wars, this article draws out the policy implications of my own empirically-based work on the role of bias in the mediation of internal armed conflicts. This article suggests that neutrality should not be part of the definition of mediators, and that instead type and degree of bias should be treated as independent variables. In fact, my research has shown that biased mediators, under some conditions, outperform neutral mediators, and also importantly, that it matters in civil wars to which side the mediator is biased: for the government or for the rebel-side. This does not imply that neutral mediators have no role to play in peacemaking processes around the globe: this article discusses explicitly the implications of my research on how neutral mediators should engage themselves in order to bring about peace in civil wars. The article also discusses the notion of âinsider-partialâ, that is, third party actors within the conflict societies and it suggested that it is important to tap these domestic resources for peace
Dystocia and caesarean section on guinea pigs in Sweden : an interview study on Swedish clinicsâ routines regarding anaesthesia, analgesia and surgical procedure
Dystoki och drÀktighetstoxikos Àr relativt vanligt förekommande problem hos marsvin förknippat
med hög mortalitet bÄde för modern och ungarna. Olika profylaktiska ÄtgÀrder och att para marsvinen innan blygdbensfogen sammanvÀxer Àr bÀsta sÀttet att förhindra drÀktighetskomplikationer. Vid
dystoki Àr kejsarsnitt ofta en sista utvÀg men om orsaken Àr vÀrksvaghet kan försök med medicinsk
behandling ha en effekt förutsatt att förlossningsvÀgarna Àr fria. Det finns mÀngder av tÀnkbara protokoll för analgesi och anestesi med olika för- och nackdelar. Utmaningar som uppstÄr med vÄrden
kring marsvin inkluderar bl.a. kÀnslighet för stress och smÀrta, upprÀtthÄllandet av normotermi, intubering, kateterisering och blodprovstagning.
Syftet med denna studie Àr att kartlÀgga rutiner kring anestesi och kejsarsnitt pÄ marsvin som
utförs i Sverige. Förhoppningen Àr att resultatet kan lÀggas till grund för fortbildningen av veterinÀrer och narkossköterskor i arbetet mot en bÀttre vÄrd för marsvinen.
Totalt fem intervjuer genomfördes med veterinÀrer varav tre medverkade pÄ en fullstÀndig intervju, en svarade pÄ ett fÄtal utvalda frÄgor och en intervjuades om rutiner kring anestesin. Resultatet av denna studie visar att rutinerna skiljer sig en del i valet av diagnostik, anestesi och analgesi
medan den kirurgiska tekniken till stor del Àr densamma. Rutinen beror mycket pÄ det akuta tillstÄndet och vikten av att inte stressa marsvinet för mycket eller Äsamka onödigt lidande. Det anses ibland
bÀttre att vÀnta med smÀrtlindring eller undvika helt för att uppnÄ en snabbare ÄtgÀrd och för att inte
pÄverka ungarna via placenta eller mjölken. Respondenterna i denna studie Àr noga med att ge hemgÄngsrÄd till djurÀgaren dÀr viktiga punkter Àr sÄrkontroll, stödmatning, att följa vikten pÄ ungarna
och att höra av sig om komplikationer tillstöter. En slutats av studien Àr att det Àven bör lÀggas ett
större fokus pÄ utbildning av djurÀgare gÀllande ansvaret att Àga marsvin.Dystocia and toxaemia of pregnancy are relatively common problems in guinea pigs associated with
high mortality both for the mother and cubs. Prophylactic interventions and to breed the guinea pig
prior to the fusion of the pubic symphysis are deemed the best ways to prevent birth-related complications. In case of dystocia, caesarean section is often the last resort, but if the cause is uterine inertia,
medicinal treatment may prove successful provided that the birth canal is not obstructed. There are
many available protocols for anaesthesia and analgesia with different pros and cons. Challenges that
arise when treating guinea pigs include inability to handle stress and pain, maintaining normothermia, intubation, catheterization and blood sampling.
The aim of this study is to map the routines regarding anaesthesia and caesarean section performed on guinea pigs in Sweden. Hopefully the results can be of use in the education of veterinarians and veterinary nurses and in the improvement of the care for guinea pigs.
A total of five interviews were performed with different veterinarians of which three were fullscale, one was shortened to a few selected questions and one interview was limited to routines regarding anaesthesia. The results show that the routines differ somewhat regarding the choice of
diagnostics, anaesthesia and analgesia, while the surgical intervention remains mostly the same. The
choice of surgical routine largely depends on the acute aspect and to avoid stressing the animal too
much or to cause unnecessary pain. It is sometimes better to postpone the analgesics or even forego
them completely to achieve the fastest treatment and not to influence the cubs via the placenta or
milk. The respondents are meticulous in handing out postoperative advice to the owners, including
wound inspection, supportive feeding, registering the weight of the cubs, and to contact the clinic if
complications arise. A conclusion was that more focus should be on educating owners regarding the
responsibility of owning a guinea pig
Vibration response of long cable-stayed timber footbridge â case study
Timber footbridges with a span larger than 30 meters are sensitive to vibrations and dynamic factors must therefore be taken into considerations in the design. A case study of a cable-stayed footbridge, Ălvsbacka Bridge, with a free span of 130 meters, is presented. The dynamic design of the bridge is compared, based on the old Swedish code, BRO 2004 and the Eurocode 5. Simplified force models presented in BRO 2004 and the ISO 10137 international standard are compared. Vertical and lateral accelerations are measured on the bridge with accelerometers attached to the bridge deck. According to the simplified force model, the vertical acceleration limit was met for a group of twenty pedestrians, which was regarded as a reasonable design situation. From the measured accelerations, the damping factor was calculated as 1.2% of critical damping, which is twice the value used in design
Larvterapi
SÄrlÀkningens grundprinciper finns dokumenterat sedan flera tusen Är tillbaka. MÄnga metoder som anvÀndes dÄ Àr idag förÄldrade men det finns substanser som moderniserats och förfinats, som t.ex. honung. Med introduktionen av antibiotika och massframstÀllningen av penicillin pÄ 1940-talet glömdes mÄnga gamla sÄrlÀkningsmetoder bort. En av dessa metoder var larvterapi som finns beskrivet i detalj av en amerikansk lÀkare pÄ 30-talet. Enligt lÀkaren verkade larverna lovande i behandlingen av nekrotiska sÄr men metoden hann inte fÄ genomslag innan penicillinet stal
rampljuset.
Nu pÄ senare tid har antibiotikaresistens hos bakterier uppmÀrksammats och man fruktar dagen dÄ antibiotika inte lÀngre har nÄgon avdödande effekt. Multiresistenta bakterier Àr inget skÀmt. Nya lÀkemedel Àr komplicerat att framstÀlla vilket gör att man försöker minska anvÀndningen av dem och pÄ sÄ sÀtt minska resistensutveckling. Alternativa behandlingar Àr eftersökta och larvterapi har mÄnga förutsÀttningar att vara en av dem.
Med tanke pÄ resistenslÀget och att sÄrlÀkning med konventionella metoder inte alltid Àr optimal vÀcks frÄgan om det finns alternativ som Àr bÀttre, exempelvis larvterapi. Forskning om verkningsmekanismer, jÀmförande studier och rapporter om kliniska fall stödjer resonemanget om att hydrogel, en konventionell metod, i vissa aspekter Àr sÀmre Àn larvterapi. Hydrogelen hjÀlper endast till genom att luckra upp nekrotisk vÀvnad och stimulera bildandet av bindvÀv. Larvernas utformning och utsöndring pÄverkar mÄnga fler ingÄende komponenter i sÄrlÀkningen. Debridering sker bÄde mekaniskt med munkrokar och hÄrdheter lÀngs kroppen och kemiskt med enzymer. Desinficering sker genom att larverna kÀkar upp patogener och avdödar de med antibakteriella substanser i magtarmkanalen. Sekretet som utsöndras minskar Àven inflammation och stimulerar sÄrlÀkning, dÀr vissa bestÄndsdelar pÄvisats vara allantoin och MAE-P6. En annan fördel som larverna har Àr den relativt lÄga kostnaden och simpla framstÀllningen. Nackdelar Àr det korta bÀst före-datumet och ovana hos utövarna som leder till felaktig applicering eller att djur lyckas fÄ av förbanden.
Det lilla utbudet pĂ„ noggranna och omfattande studier gör det svĂ„rt att med sĂ€kerhet bedöma larvernas anvĂ€ndbarhet. Dock visar mĂ„nga av de studier som finns att larvterapi i mĂ„ngt och mycket Ă€r bĂ€ttre Ă€n konventionella metoder nĂ€r det kommer till debridering och tid till sĂ„ret börjar lĂ€ka. Mer forskning behövs, i synnerhet pĂ„ de antibakteriella och anti-inflammatoriska substanserna som Ă€r medverkande skĂ€l till larvterapins framgĂ„ng.The basic principles of wound healing can be found documented several thousand years ago. Many methods from that time are outdated today, but there are substances which have been modernized and refined, for example honey. With the introduction of antibiotics and the mass production of penicillin in the 1940âs, many old methods of wound treatment were forgotten. One of these methods was larval therapy which is described in detail by an American doctor in the 1930âs. According to the doctor, larval therapy seemed promising in the treatment of necrotic wounds, but the method didnât quite catch on before the limelight was stolen by penicillin.
In recent times, antibiotic resistance in bacteria is getting more and more attention and the fear of having no effective medication against these threats is real. Multi-resistant organisms are not to be trifled with. New drugs are hard to produce which makes reducing the usage of antibiotics and therefore the development of resistance even more important. Alternative treatments are sought after, and larval therapy might just fit the bill.
Considering the current state of antibiotic resistance and that wound treatment by conventional means might not be ideal, it begs the question if there exist better alternatives, for example larval therapy. Research on mechanisms of action, comparative studies, and rapports from clinical cases supports the claim that hydrogel, a conventional method, in some respects is inferior to larval therapy. Hydrogel only softens and loosens necrotic tissue and help stimulate the formation of connective tissue. The shape and secretion of the larvae affects considerably more elements in wound healing. Debridement is both mechanical through specialized mouth hooks and minute spines on their bodies, and chemical through the release of enzymes. Disinfection is achieved when pathogens ingested by the larvae are destroyed by antibacterial substances present in the gut and intestines. The secrete also dampens inflammation and stimulates wound healing. Two important components of the secrete have been identified as allantoin and MAE-P6. Some other benefits of larval therapy are the relatively low cost and simple manufacturing process. Disadvantages are the short shelf life and practitionersâ unfamiliarity with the medium, which leads to incorrect application or enabling the treated animals getting the bandages off.
The limited selection of thoroughly executed and extensive studies makes it difficult to evaluate the usefulness of larval therapy with certainty. However, many of the present studies show that larval therapy surpasses conventional means when it comes to debridement and the time it takes for the wound to start its healing process. More research is needed, especially on the antibacterial and anti-inflammatory substances which are heavy factors behind the success of larval therapy
Bayesian parameter estimation in chiral effective field theory using the Hamiltonian Monte Carlo method
The number of low-energy constants (LECs) in chiral effective field theory (chi EFT) grows rapidly with increasing chiral order, necessitating the use of Markov chain Monte Carlo techniques for sampling their posterior probability density function. For this we introduce a Hamiltonian Monte Carlo (HMC) algorithm and sample the LEC posterior up to next-to-next-to-leading order (NNLO) in the two-nucleon sector of chi EFT. We find that the sampling efficiency of HMC is three to six times higher compared to an affine-invariant sampling algorithm. We analyze the empirical coverage probability and validate that the NNLO model yields predictions for two-nucleon scattering data with largely reliable credible intervals, provided that one ignores the leading-order EFT expansion parameter when inferring the variance of the truncation error. We also find that the NNLO truncation error dominates the error budget
Bayesian estimation of the low-energy constants up to fourth order in the nucleon-nucleon sector of chiral effective field theory
We use Bayesian methods and Hamiltonian Monte Carlo (HMC) sampling to infer the posterior probability density function (PDF) for the low-energy constants (LECs) up to next-to-next-to-next-to-leading order (N3LO) in a chiral effective field theory (ÏEFT) description of the nucleon-nucleon interaction. In a first step, we condition the inference on neutron-proton and proton-proton scattering data and account for uncorrelated ÏEFT truncation errors. We demonstrate how to successfully sample the 31-dimensional space of LECs at N3LO using a revised HMC inference protocol. In a second step we extend the analysis by means of importance sampling and an empirical determination of the neutron-neutron scattering length to infer the posterior PDF for the leading charge-dependent contact LEC in the S01 neutron-neutron interaction channel. While doing so we account for the ÏEFT truncation error via a conjugate prior. We use the resulting posterior PDF to sample the posterior predictive distributions for the effective range parameters in the S01 wave as well as the strengths of charge-symmetry breaking and charge-independence breaking. We conclude that empirical point-estimate results of isospin breaking in the S01 channel are consistent with the PDFs obtained in our Bayesian analysis and that, when accounting for ÏEFT truncation errors, one must go to next-to-next-to-leading order to confidently detect isospin breaking effects
You can have your ensemble and run it too -- Deep Ensembles Spread Over Time
Ensembles of independently trained deep neural networks yield uncertainty
estimates that rival Bayesian networks in performance. They also offer sizable
improvements in terms of predictive performance over single models. However,
deep ensembles are not commonly used in environments with limited computational
budget -- such as autonomous driving -- since the complexity grows linearly
with the number of ensemble members. An important observation that can be made
for robotics applications, such as autonomous driving, is that data is
typically sequential. For instance, when an object is to be recognized, an
autonomous vehicle typically observes a sequence of images, rather than a
single image. This raises the question, could the deep ensemble be spread over
time?
In this work, we propose and analyze Deep Ensembles Spread Over Time (DESOT).
The idea is to apply only a single ensemble member to each data point in the
sequence, and fuse the predictions over a sequence of data points. We implement
and experiment with DESOT for traffic sign classification, where sequences of
tracked image patches are to be classified. We find that DESOT obtains the
benefits of deep ensembles, in terms of predictive and uncertainty estimation
performance, while avoiding the added computational cost. Moreover, DESOT is
simple to implement and does not require sequences during training. Finally, we
find that DESOT, like deep ensembles, outperform single models for
out-of-distribution detection
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