Using rational expectations storage model to explain natural gas price

Natural gas is a key energy source for residential, commercial, electric power and industrial use. Residential, commercial and electric power sector consumption is primarily driven by weather conditions and displays obvious seasonal patterns while production is relatively stable throughout the year. As weather condition is uncertain and both consumption and production are inelastic in the short term, natural gas price is quite volatile especially in the heating season. Due to an imbalance between production and consumption, storage plays an important role in ensuring availability and smoothing price between low and peak consumption seasons. Storage is also a key driver of price volatility. The existing literature confirms the importance of inventory and weather conditions in determining price and its variance. Most studies to date use time series models and focus on the historical price realizations while providing little insight into how price patterns are determined by market participants’ behavior. In addition, the impact of inventory and weather variables on price volatility has not been analyzed in detail. This thesis aims to construct a model that can mimic the major market participants’ behavior and reproduce the natural gas price with mean and standard deviation patterns consistent with historical observations: higher average level and standard deviation in peak consumption season. We construct a monthly rational-expectations competitive storage model to better reflect monthly variations in price. Natural gas consumption and production are specified in a way that the current period volume is highly correlated with previous period volume so as to capture the stickiness and gradual change in natural gas markets. Imposing non-arbitrage condition, price is inter-temporally correlated. Net storage cost consists of both physical storage cost and convenience yield obtained from holding stock at hand. Normal storage level for each month is introduced to reflect the yearly cycling of natural gas inventory and is used in the convenience yield calibration. It denotes the normal storage level each month that is needed to balance seasonal demand-supply relationship. Convenience yield is high if the inventory falls below normal storage level and high convenience yield pushes up the price and decreases current consumption to accumulate more natural gas for future use. The model is solved using numerical methods because analytical solutions are not feasible. In order to validate the result, accuracy tests are conducted and the major assumptions are tested as well. The model’s approximation errors are reasonable. The model is further validated by comparing simulated price series with historical observations by using historical weather variables in the solved model. The simulated model generates prices that largely replicate the key features of historical data, including the price level, price variance, price sensitivity under unusual weather conditions and price autocorrelation. Weather conditions and total natural gas availability are the main drivers for price and price standard deviation. The model finds that in winter high heating degree days (HDD) or low inventory drives price and price volatility higher while price and its variance decrease with low HDD and high inventory. The case is similar in summer with cooling degree days (CDD) instead of HDD as the weather variable. When inventory is low, weather shocks have a larger impact on price than when inventory is high. The effect is more pronounced in winter than in summer because the supply is tighter in heating season. Using the validated competitive storage model, this thesis further assesses the potential impact of LNG export on the U.S. domestic natural gas market. Given the large pricing spread between the United States and the rest of world, along with policy promotion and the completion of LNG facilities, U.S. LNG exports are poised to expand dramatically. This study covers two major types of LNG export scenarios: exogenous fixed volume and endogenous export volume depending on the price spread between US and world prices. Four export scenarios are analyzed and compared with the benchmark scenario of no LNG export. The first two scenarios are fixed export volume with 6 bcf/day and 12 bcf/day respectively, to be consistent and comparable with an EIA 2014 report and the existing literature. One of the endogenous scenario scenarios assumes no consumption and supply growth for importing countries and the other one assume 100% increase of demand and 50% increase of supply in LNG importing countries by 2036. Because of high shipping cost and inelastic natural gas demand in importing countries, the U.S. LNG is not competitive under current market condition, if no growth is expected. The U.S. LNG export volume is very small and decreases over time. Due to small export volumes, the domestic price impact is minimal. For all scenarios analyzed in this study, the long-term price impact is less than 8%, or around $0.33 per thousand cubic feet. In the long-term, the endogenous export with growth assumption scenario shows the largest price increase compared to the no export benchmark scenario. The export level is around 12 bcf per day. The U.S. domestic price variance becomes smaller if an endogenous export sector is added while the price variance becomes higher under fixed export volume scenarios. If the LNG export is endogenously determined, when domestic price increased, LNG export decreases. This provides an additional buffer to the U.S. domestic market if there is shock to push up natural gas consumption and price. In contrast, fixed volume export makes the total natural gas consumption less responsive to price change and thus increases price variance. Most of the LNG export volumes will be satisfied by production increases instead of domestic consumption reductions in the long term. In all four scenarios analyzed in this study, production catches up gradually in response to price increase due to LNG export. In the beginning period when production is constrained by production capacity, most of the export is covered by domestic consumption reduction. In the long term, as production increase, domestic consumption recovers to similar level as in the no export scenario

The immune mechanism of the nasal epithelium in COVID-19–related olfactory dysfunction

During the first waves of the coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, olfactory dysfunction (OD) was reported as a frequent clinical sign. The nasal epithelium is one of the front-line protections against viral infections, and the immune responses of the nasal mucosa may be associated with OD. Two mechanisms underlying OD occurrence in COVID-19 have been proposed: the infection of sustentacular cells and the inflammatory reaction of the nasal epithelium. The former triggers OD and the latter likely prolongs OD. These two alternative mechanisms may act in parallel; the infection of sustentacular cells is more important for OD occurrence because sustentacular cells are more likely to be the entry point of SARS-CoV-2 than olfactory neurons and more susceptible to early injury. Furthermore, sustentacular cells abundantly express transmembrane protease, serine 2 (TMPRSS2) and play a major role in the olfactory epithelium. OD occurrence in COVID-19 has revealed crucial roles of sustentacular cells. This review aims to elucidate how immune responses of the nasal epithelium contribute to COVID-19–related OD. Understanding the underlying immune mechanisms of the nasal epithelium in OD may aid in the development of improved medical treatments for COVID-19–related OD

VHL inactivation in renal cell carcinoma: implications for diagnosis, prognosis and treatment

Clear cell renal cell carcinoma (ccRCC) provides a tumor paradigm for the integration of genetics, molecular biology, therapeutic target validation, and the introduction of high impact treatment strategies. Most cases of sporadic as well as familial ccRCC acquire somatic inactivating mutations of the von Hippel-Lindau tumor suppressor gene, VHL. pVHL, VHL gene product and a protein member of the E3 ubiquitin ligase family, acts in normal cells to direct the degradation and clearance of the hypoxia inducible factor (HIFα) transcription factor family, such that in its absence, as in ccRCC, the HIF proteins stabilize, accumulate to supraphysiologic levels, and activate the transcription of genes such as vascular endothelial growth factor (VEGF) and platelet derived growth factor (PDGF), which contributes substantially to the physiology of the tumor, and has been assessed indirectly as a prognostic factor. Molecularly targeted therapy blocking components of this pathway has been successfully introduced to the clinic with a substantive impact on clinical parameters of RCC. This review will examine the regulation of these molecular pathways in RCC and discuss the impact on the clinical management of patients with RCC

Energy Stable Numerical Schemes for Ternary Cahn-Hilliard System

We present and analyze a uniquely solvable and unconditionally energy stable numerical scheme for the ternary Cahn-Hilliard system, with a polynomial pattern nonlinear free energy expansion. One key difficulty is associated with presence of the three mass components, though a total mass constraint reduces this to two components. Another numerical challenge is to ensure the energy stability for the nonlinear energy functional in the mixed product form, which turns out to be non-convex, non-concave in the three-phase space. to overcome this subtle difficulty, we add a few auxiliary terms to make the combined energy functional convex in the three-phase space, and this, in turn, yields a convex-concave decomposition of the physical energy in the ternary system. Consequently, both the unique solvability and the unconditional energy stability of the proposed numerical scheme are established at a theoretical level. in addition, an optimal rate convergence analysis in the ℓ∞(0,T;HN-1)∩ℓ2(0,T;HN1) norm is provided, with Fourier pseudo-spectral discretization in space, which is the first such result in this field. to deal with the nonlinear implicit equations at each time step, we apply an efficient preconditioned steepest descent (PSD) algorithm. a second order accurate, modified BDF scheme is also discussed. a few numerical results are presented, which confirm the stability and accuracy of the proposed numerical scheme

Evaluating the Efficacy of VitalStim Electrical Stimulation Combined with Swallowing Function Training for Treating Dysphagia following an Acute Stroke

OBJECTIVES: This study explored the clinical efficacy of VitalStim electrical stimulation combined with swallowing function training for patients with dysphagia following an acute stroke. METHODS: Seventy-two patients with dysphagia following an acute stroke were admitted to our hospital and were further divided into two groups using prospective research methods. There were 36 cases in each group according to the random number table method. The control group received conventional medical treatment and swallowing function training while the experimental group received conventional medical treatment and VitalStim electrical stimulation combined with swallowing function training. RESULTS: The overall response rate of the experimental group (94.44%) was higher than that of the control group (77.78%), and the difference was statistically significant (p<0.05). Compared with before treatment, the upward and forward movement speeds of the hyoid bone, anterior movement speed, the grading score of the Kubota drinking water test, Caiteng's grading score, serum superoxide dismutase, 5-hydroxytryptamine, and norepinephrine levels, Fugl-Meyer Assessment score, and multiple quality of life scores of the two groups showed improvement after treatment. While the standard swallowing assessment score, serum malondialdehyde level, and National Institutes of Health Stroke Scale score decreased, the aforementioned indices showed a significant improvement in the experimental group (p<0.05). CONCLUSION: The results of this study indicate that VitalStim electrical stimulation combined with swallowing function is effective for treating dysphagia following an acute stroke. It can effectively improve swallowing, neurological, and limb motor functions, reduce complications, promote physical recovery, and improve overall quality of life of patients

Error Estimate of a Decoupled Numerical Scheme for the Cahn-Hilliard-Stokes-Darcy System

We analyze a fully discrete finite element numerical scheme for the Cahn-Hilliard-Stokes-Darcy system that models two-phase flows in coupled free flow and porous media. To avoid a well-known difficulty associated with the coupling between the Cahn-Hilliard equation and the fluid motion, we make use of the operator-splitting in the numerical scheme, so that these two solvers are decoupled, which in turn would greatly improve the computational efficiency. The unique solvability and the energy stability have been proved in Chen et al. (2017, Uniquely solvable and energy stable decoupled numerical schemes for the Cahn-Hilliard-Stokes-Darcy system for two-phase flows in karstic geometry. Numer. Math., 137, 229-255). In this work, we carry out a detailed convergence analysis and error estimate for the fully discrete finite element scheme, so that the optimal rate convergence order is established in the energy norm, i.e., in the ℓ ∞(0, T; H1) ∩2 (0, T; H2) norm for the phase variables, as well as in the ℓ ∞ (0, T; H1) ∩ ℓ2 (0, T; H2) norm for the velocity variable. Such an energy norm error estimate leads to a cancelation of a nonlinear error term associated with the convection part, which turns out to be a key step to pass through the analysis. In addition, a discrete ℓ2 (0;T; H3) bound of the numerical solution for the phase variables plays an important role in the error estimate, which is accomplished via a discrete version of Gagliardo-Nirenberg inequality in the finite element setting

Long-chain acyl-CoA synthetase isoforms differ in preferences for eicosanoid species and long-chain fatty acids

Because the signaling eicosanoids, epoxyeicosatrienoic acids (EETs) and HETEs, are esterified to membrane phospholipids, we asked which long-chain acyl-CoA synthetase (ACSL) isoforms would activate these molecules and whether the apparent FA substrate preferences of each ACSL isoform might differ depending on whether it was assayed in mammalian cell membranes or as a purified bacterial recombinant protein. We found that all five ACSL isoforms were able to use EETs and HETEs as substrates and showed by LC-MS/MS that ACSLs produce EET-CoAs. We found differences in substrate preference between ACS assays performed in COS7 cell membranes and recombinant purified proteins. Similarly, preferences and Michaelis-Menten kinetics for long-chain FAs were distinctive. Substrate preferences identified for the purified ACSLs did not correspond to those observed in ACSL-deficient mouse models. Taken together, these data support the concept that each ACSL isoform exhibits a distinct substrate preference, but apparent substrate specificities depend upon multiple factors including membrane character, coactivators, inhibitors, protein interactions, and posttranslational modification

Inhibition of microRNA-376b Protects Against Renal Interstitial Fibrosis via Inducing Macrophage Autophagy by Upregulating Atg5 in Mice with Chronic Kidney Disease

Background/Aims: Renal interstitial fibrosis (RIF) is a common feature that facilitates the progression of chronic kidney disease (CKD), and emerging lines of evidence suggest that microRNA-376b (miR-376b) is capable of promoting RIF. In this study, we examined collagen deposition in kidney tissues, the autophagy and mitochondrial reactive oxygen species (ROS) of macrophages, and the apoptosis of kidney fibroblasts (KFBs) after the promotion or suppression of endogenous miR-376b in cultured macrophages and renal fibroblasts obtained from mice with CKD. Methods: FVB/N mice were prepared to establish a CKD model. A target prediction program and luciferase activity determination were used to confirm that autophagy-related gene 5 (Atg5) was a direct target of miR-376b. Macrophages and KFBs were isolated after the treatment to study the mechanisms and functions of miR-376b in relation to Atg5 in CKD. The autophagy level was determined, and KFB proliferation and apoptosis were assessed through MTT and EdU assays and flow cytometry, respectively. Results: Atg5 was confirmed as a direct target of miR-376b. miR-376b and Atg5 exhibited high and low expression in kidney tissues from mice with CKD. The mice treated with a miR-376b inhibitor exhibited reduced collagen deposition, suppressed interstitial fibrosis, a higher level of autophagy, higher ROS production, enhanced apoptosis, and inhibited proliferation of KFBs, which suggested that the downregulation of miR-376b could exert beneficial effects on CKD through Atg5. Conclusion: miR-376b downregulation promotes macrophage autophagy to relieve RIF by negatively regulating Atg5 in mice with CKD. Thus, miR-376b might represent a potential focus of future investigations on treatments for CKD

Effects of tropospheric ozone pollution on net primary productivity and carbon storage in terrestrial ecosystems of China

Author Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 112 (2007): D22S09, doi:10.1029/2007JD008521.We investigated the potential effects of elevated ozone (O3) along with climate variability, increasing CO2, and land use change on net primary productivity (NPP) and carbon storage in China's terrestrial ecosystems for the period 1961–2000 with a process-based Dynamic Land Ecosystem Model (DLEM) forced by the gridded data of historical tropospheric O3 and other environmental factors. The simulated results showed that elevated O3 could result in a mean 4.5% reduction in NPP and 0.9% reduction in total carbon storage nationwide from 1961 to 2000. The reduction of carbon storage varied from 0.1 Tg C to 312 Tg C (a decreased rate ranging from 0.2% to 6.9%) among plant functional types. The effects of tropospheric O3 on NPP were strongest in east-central China. Significant reductions in NPP occurred in northeastern and central China where a large proportion of cropland is distributed. The O3 effects on carbon fluxes and storage are dependent upon other environmental factors. Therefore direct and indirect effects of O3, as well as interactive effects with other environmental factors, should be taken into account in order to accurately assess the regional carbon budget in China. The results showed that the adverse influences of increasing O3 concentration across China on NPP could be an important disturbance factor on carbon storage in the near future, and the improvement of air quality in China could enhance the capability of China's terrestrial ecosystems to sequester more atmospheric CO2. Our estimation of O3 impacts on NPP and carbon storage in China, however, must be used with caution because of the limitation of historical tropospheric O3 data and other uncertainties associated with model parameters and field experiments.This research is funded by NASA Interdisciplinary Science Program (NNG04GM39C)