Mixed Unit Roots and Deterministic Trends in Noncausality Tests

Using Japanese economic data and a Monte Carlo simulation, this study analyzes the consequences of ignoring deterministic trends in mixed unit-root data for Granger noncausality tests. Results from an augmented VAR suggest over-rejection in certain empirically relevant cases at various sample sizes.Research Methods/ Statistical Methods,

Searching for Low Mass Dark Portal at the LHC

Light dark matter with mass smaller than about 10 GeV is difficult to probe from direct detection experiments. In order to have the correct thermal relic abundance, the mediator of the interaction between dark matter and the Standard Model (SM) should also be relatively light, $\sim 10^2$ GeV. If such a light mediator couples to charged leptons, it would already be strongly constrained by direct searches at colliders. In this work, we consider the scenario of a leptophobic light $Z'$ vector boson as the mediator, and study the the prospect of searching for it at the 8 TeV Large Hadron Collider (LHC). To improve the reach in the low mass region, we perform a detailed study of the processes that the $Z'$ is produced in association with jet, photon, $W^\pm$ and $Z^0$. We show that in the region where the mass of $Z'$ is between 80 and 400 GeV, the constraint from associated production can be comparable or even stronger than the known monojet and dijet constraints. Searches in these channels can be complementary to the monojet search, in particular if the $Z'$ couplings to quarks ($g_{Z'}$) and dark matter ($g_D$) are different. For $g_D < g_{Z'}$, we show that there is a larger region of parameter space which has correct thermal relic abundance and a light $Z'$, $M_{Z'} \sim 100$ GeV. This region, which cannot be covered by the mono-jet search, can be covered by the resonance searches described in this paper.Comment: 16 pages, 5 figure

Three papers on the behavior modeling of the shrimp fishermen in the Gulf of Mexico

The overall goal of this research is to empirically analyze shrimp fishermen behavior to help improve the management of the Gulf of Mexico shrimp fleet. Given that optimal management requires consideration of more than the net benefits derived from shrimp harvesting, this research also seeks to provide an empirical framework that would allow future investigators to measure benefits lost through bycatch-related management actions. This paper expands on previous fishing behavior literature by focusing on two of the most important short-run decisions confronting Gulf of Mexico shrimp fishermen (where to fish and how long to fish). A better understanding of these factors can provide useful information to policy makers in designing and implementing more effective policies. This study uses panel data for up to 15 years, which is a combination of the Coast Guard Vessel Operating Unit File and the Shrimp Landing File from National Marine Fisheries Service. In the location choice analyses, the U.S. Gulf of Mexico is divided into three areas: FL, LAM, and TX. For each area a conditional logit and mixed logit based on Random Utility Model are run to analyze the influence of fishermen’s past choice decision on current choice (state dependence), and the fishermen’s difference in preferences (preference heterogeneity). The results show that past experience does affect current decision, but the influence dies out fast. In addition, fishers are different in their preference in many aspects. Also, it seems that fishermen’s risk attitudes can change over the years. Their tolerance towards congestion exhibits changes over time too. As for their trip length decision, it seems that diesel price is negatively related to the length of days fished, so is the price difference between large and medium sized shrimp. Further, there seems to be a pattern that the trip length is increasing over the years. The incorporation of unobserved heterogeneity into the location choice and duration models corrects the potential biasedness in estimates and improves the goodness-of-fit considerably, aside from provides intuitive economic interpretations

Nutrient and organic matter removal from wastewaters with microalgae

Mikroleviä voidaan hyödyntää jätevesien käsittelyssä nykyisten käsittelyjärjestelmien yh-teydessä tai kokonaan korvaamaan nykyiset käsittelymenetelmät ravinteiden ja muiden epäpuhtauksien poistossa. Jätevedenkäsittelyn ja mikrolevien kasvatuksen yhdistämi-nen mahdollistaa typen ja fosforin talteenoton ja samanaikaisesti tuotetun mikroleväbio-massan hyödyntämisen esimerkiksi biopolttoaineiden ja/tai lannoitteiden raaka-aineena. Mikrolevien käyttö jätevedenkäsittelyssä vaatii kuitenkin vielä tutkimus- ja kehitystyötä ravinteiden poistotehokkuuden ja mikrolevien kasvun tehostamiseksi. Tämän väitöskir-jan tavoitteena oli mahdollistaa tehokas ravinteiden ja orgaanisen aineksen poisto jäte-vesistä edistäen samalla mikrolevien tehokasta kasvua. Laboratoriomittakaavan fotobioreaktoreissa tehdyissä panoskokeissa Chlorella vulgaris ja Scenedesmus acuminatus mikrolevien todettiin kasvavan sekä kunnallisen (ADMW) että sellu- ja paperitehtaan (ADPP) jätevedenpuhdistamon ylijäämälietteen mädätyksen rejektivesissä. Kummankin levän avulla pystyttiin poistamaan yli 97% ADPP:n sisältä-mästä ammoniumista, mutta ADMW:sta ammoniumpoistotehokkuus oli vain 24 % kas-vatettaessa C. vulgaris mikrolevää ja 44 % kasvatettaessa S. acuminatus mikrolevää. Molempien mikrolevien fosforinpoistotehokkuus kummastakin rejektivedestä oli yli 96 %. Myös väriä (74-80 %) ja kemiallinen hapenkulutusta (27-39 %) saatiin vähennettyä. Kokeissa ADPP:ssa saavutetut S. acuminatus biomassakonsentraatiot (7,8-10,8 g L-1 VSS) ovat korkeimpien joukossa, kun vertaillaan oikeita jätevesiä käytettäessä kirjalli-suudessa raportoituja mikroleväbiomassasaantoja. Vertailtaessa S. acuminatus mikro-levän kasvua eri mädätysolosuhteissa tuotetuissa ADPP rejektivesissä, suurin S. acu-minatus biomassakonsentraatio saavutettiin termofiilisen mädätyksen rejektivesissä. Il-man esikäsittelyä ennen termofiilistä mädätystä korkein biomassakonsentraatio oli 10,2 ± 2,2 g L-1 ja esikäsittelyn sisältäneen termofiilisen mädätyksen rejektivedessä 10,8 ± 1,2 g L-1. Esikäsittelyn sisältäneen mesofiilisen mädätyksen ADPP-rejektivedessä suurin S. acuminatus biomassakonsentraatio oli 7,8 ± 0,3 g L-1. Myös korkein metaanin tuotto saa-vutettiin esikäsittelyn sisältäneessä termofiilisessä mädätysprosessissa, mikä osoittaa, että tehokkain metaanin tuotto ja mikrolevien biomassatuotto saavutettiin samoissa pro-sessiolosuhteissa. Raudan (0,1; 1,0 ja 1,9 mg L-1) ja sulfaatti- rikin (3;7; 20 ja 35,8 mg L-1) pitoisuuksien havaittiin vaikuttavan typen poistotehokkuuteen ja mikrolevien biomassakonsentraatioon enemmän typenlähteen ollessa nitraatti kuin käytettäessä ammoniumia typenlähteenä. Korkein S. acuminatus biomassakonsentraatio saavutettiin nitraattipohjaisessa kasva-tusmediassa, jossa oli 1,0 mg L-1-rautaa ja 35,8 mg L-1 rikkiä. Rautakonsentraatio vaikutti mikrolevien kasvuun ja typenpoistotehokkuuteen enemmän kuin sulfaattipitoisuus. Rau-dalla ja rikillä ei havaittu olevan yhteisvaikutusta. Mikrolevien kasvua pyrittiin tehostamaan lisäämällä jatkuvatoimiseen membraanifoto-bioreaktoriin eri määriä zeoliiittia. Kun zeoliittia lisättiin 0,5 g L-1, keskimääräinen ammo-niumin poistotehokkuus nousi 14 %:sta 30 %:iin ja biomassakonsentraatio 0.5 g L-1:sta yli 1,0 g L-1:aan. Havaitun tehokkuuden lisääntymisen uskottiin johtuvan siitä, että zeoliitti tarjosi pinnan, jolla mikrolevien havaittiin kasvavan. Lisäksi zeoliitin on osoitettu adsor-boivan ammoniumia ympäröivästä vedestä. Reaktorin zeoliittikonsentraation nostami-nen 0.5 g L-1:sta 1g L-1:aan ja myöhemmin 5 g L-1:aan ei kuitenkaan enää kasvattanut ammoniumin poistotehokkuutta tai biomassakonsentraatiota. Tämä johtui todennäköisesti zeoliittipartikkelien hajoamisesta hienommiksi hiukkasiksi, mikä hei-kensi valon saatavuutta. Tutkimus osoitti, että mikroleviä voidaan hyödyntää jätevedenpuhdistuksessa ravintei-den talteenottoon ja samalla kasvattaa tehokkaasti mikroleväbiomassaa. On kuitenkin tärkeää valita kullekin jätevedelle soveltuva mikrolevälaji, jotta prosessi toimisi tehokkaasti.Use of microalgae in wastewater treatment has been increasingly studied to integrate with or replace the present treatment systems for removal of nutrients and other pollu-tants. The potential advantages of this integration (wastewater treatment and microalgal cultivation) could be simultaneous recovery of nitrogen and phosphorus and the use of produced microalgal biomass as feedstock for e.g. biofuel, fertilizer and/or energy. How-ever, the use of microalgae in wastewater treatment is mainly in research stage due to e.g. low nutrient removal and microalgal biomass growth. The aim of this thesis was to enable efficient nutrient and organic matter removal from wastewaters by microalgae while promoting microalgal biomass production. Chlorella vulgaris and Scenedesmus acuminatus were successfully grown in batch pho-tobioreactors with liquid digestates from anaerobic digestion (AD) of biosludge from a municipal wastewater treatment plant (ADMW) and a pulp and paper mill wastewater treatment plant (ADPP). The final ammonium removal efficiencies were above 97% when cultivating both microalgae separately in ADPP, however, only 24% and 44% of ammo-nium were removed from ADMW by C. vulgaris and S. acuminatus, respectively. Both microalgae efficiently removed phosphate (>96%), while color (74–80%) and soluble COD (27–39%) were partially removed from ADMW and ADPP. The obtained highest S. acuminatus biomass concentration (7.8–10.8 g L-1 VSS) in ADPP is among the highest yields reported for microalgae in real wastewaters. Higher S. acuminatus biomass yields were obtained in thermophilic ADPP (without and with pretreatment prior to AD: 10.2±2.2 and 10.8±1.2 g L-1, respectively) than in pretreated mesophilic ADPP (7.8±0.3 g L-1). In addition, the highest microalgal biomass concentra-tion and methane yields were obtained in the same integrated AD and microalgal culti-vation system (thermophilic AD with pretreatment). The iron (0.1, 1.0, and 1.9 mg L-1) and sulfate-sulfur (3.7, 20, and 35.8 mg L-1) concen-trations were found to affect nitrogen removal efficiency and microalgal biomass concen-tration more in the media with nitrate than with ammonium, probably due to different microalgal assimilation mechanisms for nitrate and ammonium. In this study, synthetic medium with nitrate as nitrogen source with 1.0 mg L-1 iron and 35.8 mg L-1 sulfate-sulfur enabled the highest microalgal biomass concentration. The effect of iron concentration on nitrate removal efficiency and microalgal growth was more significant than that of sulfate concentration, while the interaction effect between sulfate and iron was not ob-served. The average ammonium removal efficiency (14 to 30%) and microalgal biomass concen-tration (0.50 to 1.17 g particulate organic carbon per L) in continuous-flow membrane photobioreactor were promoted by adding a low concentration of zeolite (0.5 g L-1). The zeolite likely provided a habitat for attached growth of microalgae and high availability of ammonium for growth on the surface of the zeolite due to ammonium adsorption to zeo-lite. Further increase in zeolite concentration (from 0.5 to 1 and 5 g L-1) did not improve ammonium removal efficiency or biomass concentration. This was likely due to the in-creased solution turbidity caused by breaking apart of added zeolite particles into finer particles, which reduced light availability. In summary, this work showed the possibility of utilizing microalgae in wastewater treat-ment to efficiently remove nutrients and organic matter, and simultaneously promote mi-croalgal growth. Selecting suitable microalgal species for the specific wastewater to re-move nutrients and organic matter is essential to promote algae-based wastewater treat-ment applications