Microscopic characteristics of tight sandstone reservoirs and their effects on the imbibition efficiency of fracturing fluids:A case study of the Linxing area,Ordos Basin

The Linxing area within the Ordos Basin exhibits pronounced reservoir heterogeneity and intricate micro-pore structures,rendering it susceptible to water-blocking damage during imbibition extraction.This study delved into the traits of tight sandstone reservoirs in the 8th member of the Shihezi Formation(also referred to as the He 8 Member)in the study area,as well as their effects on fracturing fluid imbibition.Utilizing experimental techniques such as nuclear magnetic resonance(NMR),high-pressure mercury intrusion(HPMI),and gas adsorption,this study elucidated the reservoir characteristics and examined the factors affecting the imbibition through imbibition experiments.The findings reveal that:①The reservoir,with average porosity of 8.40%and average permeability of 0.642×10^(-3)μm^(2),consists principally of quartz,feldspar,and lithic fragments,with feldspathic litharenite serving as the primary rock type and illite as the chief clay mineral;②Nano-scale micro-pores and throats dominate the reservoir,with dissolution pores and intercrystalline pores serving as predominant pore types,exhibiting relatively high pore connectivity;③Imbibition efficiency is influenced by petrophysical properties,clay mineral content,and microscopic pore structure.Due to the heterogeneity of the tight sandstone reservoir,microscopic factors have a more significant impact on the imbibition efficiency of fracturing fluids;④A comparative analysis shows that average pore size correlates most strongly with imbibition efficiency,followed by petrophysical properties and clay mineral content.In contrast,the pore type has minimal impact.Micropores are vital in the imbibition process,while meso-pores and macro-pores offer primary spaces for imbibition.This study offers theoretical insights and guidance for enhancing the post-fracturing production of tight sandstone reservoirs by examining the effects of these factors on the imbibition efficiency of fracturing fluids in tight sandstones.

Impact Analysis of Microscopic Defect Types on the Macroscopic Crack Propagation in Sintered Silver Nanoparticles

Sintered silver nanoparticles(AgNPs)arewidely used in high-power electronics due to their exceptional properties.However,the material reliability is significantly affected by various microscopic defects.In this work,the three primary micro-defect types at potential stress concentrations in sintered AgNPs are identified,categorized,and quantified.Molecular dynamics(MD)simulations are employed to observe the failure evolution of different microscopic defects.The dominant mechanisms responsible for this evolution are dislocation nucleation and dislocation motion.At the same time,this paper clarifies the quantitative relationship between the tensile strain amount and the failure mechanism transitions of the three defect types by defining key strain points.The impact of defect types on the failure process is also discussed.Furthermore,traction-separation curves extracted from microscopic defect evolutions serve as a bridge to connect the macro-scale model.The validity of the crack propagation model is confirmed through tensile tests.Finally,we thoroughly analyze how micro-defect types influence macro-crack propagation and attempt to find supporting evidence from the MD model.Our findings provide a multi-perspective reference for the reliability analysis of sintered AgNPs.

A review of interaction mechanisms and microscopic simulation methods for CO_(2)-water-rock system

This work systematically reviews the complex mechanisms of CO_(2)-water-rock interactions,microscopic simulations of reactive transport(dissolution,precipitation and precipitate migration)in porous media,and microscopic simulations of CO_(2)-water-rock system.The work points out the key issues in current research and provides suggestions for future research.After injection of CO_(2) into underground reservoirs,not only conventional pressure-driven flow and mass transfer processes occur,but also special physicochemical phenomena like dissolution,precipitation,and precipitate migration.The coupling of these processes causes complex changes in permeability and porosity parameters of the porous media.Pore-scale microscopic flow simulations can provide detailed information within the three-dimensional pore and throat space and explicitly observe changes in the fluid-solid interfaces of porous media during reactions.At present,the research has limitations in the decoupling of complex mechanisms,characterization of differential multi-mineral reactions,precipitation generation mechanisms and characterization(crystal nucleation and mineral detachment),simulation methods for precipitation-fluid interaction,and coupling mechanisms of multiple physicochemical processes.In future studies,it is essential to innovate experimental methods to decouple“dissolution-precipitation-precipitate migration”processes,improve the accuracy of experimental testing of minerals geochemical reaction-related parameters,build reliable characterization of various precipitation types,establish precipitation-fluid interaction simulation methods,coordinate the boundary conditions of different physicochemical processes,and,finally,achieve coupled flow simulation of“dissolution-precipitation-precipitate migration”within CO_(2)-water-rock systems.

Microscopic characteristics and geological significance of pyrite in shales of the Wufeng-Longmaxi formations,southeastern Chongqing,China

Shales of the Wufeng-Longmaxi formations in the basin-margin transition zone of southeastern Chongqing,China are characterized by high organic matter content and a significant presence of pyrite development.By examining numerous scanning electron microscope(SEM)images and considering the crystal and aggregate characteristics of minerals,we identified four types of pyrite in the study area:euhedral crystals,irregular aggregates,framboidal aggregates,and metasomatized organisms.Among these types,framboidal aggregates are the most prevalent.The formation mechanism of framboidal pyrite can be categorized into inorganic and organic origins.As inferred from the pyrite characteristics in the study area,the formation mechanism of the metasomatized organisms aligns with the biologically induced mineralization mode of organic origin,whereas the framboidal aggregates are more associated with the biologically controlled mineralization mode of organic origin.This underscores a close relationship between the pyrite formation and organic matter,which in turn indicates that an organic origin is more consistent with the pyrite characteristics observed in this study area.The pyrite morphology can reflect reactive iron concentration.Euhedral pyrite crystals tend to form under a low reactive iron concentration,whereas the formation of framboidal pyrite requires a high reactive iron concentration.Additionally,the type and grain size of pyrite aggregates can reflect variations in the redox conditions of the depositional environment.Pyrite produces positive effects on reservoir storage space,with intercrystalline organic pores,intercrystalline pores,and mold pores associated with pyrite contributing greatly to the storage spaces.

Microscopic growth mechanism and edge states of monolayer 1T'-MoTe_(2)

Transition metal ditellurides(TMTDs)have versatile physical properties,including non-trivial topology,Weyl semimetal states and unique spin texture.Controlled growth of high-quality and large-scale monolayer TMTDs with preferred crystal phases is crucial for their applications.Here,we demonstrate the epitaxial growth of 1T'-MoTe_(2) on Au(111)and graphitized silicon carbide(Gr/SiC)by molecular beam epitaxy(MBE).We investigate the morphology of the grown1T'-MoTe_(2) at the atomic level by scanning tunnelling microscopy(STM)and reveal the corresponding microscopic growth mechanism.It is found that the unique ordered Te structures preferentially deposited on Au(111)regulate the growth of monolayer single crystal 1T'-MoTe_(2),while the Mo clusters were preferentially deposited on the Gr/SiC substrate,which impedes the ordered growth of monolayer MoTe_(2).We confirm that the size of single crystal 1T'-MoTe_(2) grown on Au(111)is nearly two orders of magnitude larger than that on Gr/SiC.By scanning tunnelling spectroscopy(STS),we observe that the STS spectrum of the monolayer 1T'-MoTe_(2) nano-island at the edge is different from that at the interior,which exhibits enhanced conductivity.

Application of a microscopic optical potential of chiral effective field theory in (p, d) transfer reactions

The microscopic global nucleon–nucleus optical model potential(OMP)proposed by Whitehead,Lim,and Holt,the WLH potential(Whitehead et al.,Phys Rev Lett 127:182502,2021),which was constructed in the framework of many-body per-turbation theory with state-of-the-art nuclear interactions from chiral effective field theory(EFT),was tested with(p,d)transfer reactions calculated using adiabatic wave approximation.The target nuclei included both stable and unstable nuclei,and the incident energies reached 200 MeV.The results were compared with experimental data and predictions using the phenomenological global optical potential of Koning and Delaroche,the KD02 potential.Overall,we found that the micro-scopic WLH potential described the(p,d)reaction angular distributions similarly to the phenomenological KD02 potential;however,the former was slightly better than the latter for radioactive targets.On average,the obtained spectroscopic factors(SFs)using both microscopic and phenomenological potentials were similar when the incident energies were below approxi-mately 120 MeV.However,their difference tended to increase at higher incident energies,which was particularly apparent for the doubly magic target nucleus 40Ca.

Gold Standard for Skin Cancer Treatment: Surgery (Mohs) or Microscopic Molecular-Cellular Therapy (Curaderm)?

Non-melanoma skin cancers or keratinocyte cancers such as basal cell carcinoma and squamous cell carcinoma make up approximately 80% and 20% respectively, of skin cancers with the 6 million people that are treated annually in the United States. 1 in 5 Americans and 2 in 3 Australians develop skin cancer by the age of 70 years and in Australia it is the most expensive, amassing $1.5 billion, to treat cancers. Non-melanoma skin cancers are often self-detected and are usually removed by various means in doctors’ surgeries. Mohs micrographic surgery is acclaimed to be the gold standard for the treatment of skin cancer. However, a novel microscopic molecular-cellular non-invasive topical therapy described in this article, challenges the status of Mohs procedure for being the acclaimed gold standard.

Research Analysis on the Microscopic Properties and Damping Performance of Carbon Nanomaterial-Modified Cement Mortar

The application of carbon nanomaterials, particularly graphene and carbon nanotubes, in cement-based composites is highly significant. These materials demonstrate the multifunctionality of carbon and offer extensive possibilities for technological advancements. This research analyzes how the integration of graphene into cement-based composites enhances damping and mechanical properties, thereby contributing to the safety and durability of structures. Research on carbon nanomaterials is ongoing and is expected to continue driving innovation across various industrial sectors, promoting the sustainable development of building materials.

Recording the direct surgeon’s view with an operating microscopic view improves microscopic ophthalmic surgery training

AIM:To establish a recording system with a direct view of the surgeon to supplement video recording under an operating microscope,which lacks information on the movement and position of the surgeon’s hands,and to facilitate the reproduction of a skilled surgeon’s technique by a surgeon in training.METHODS:A small camera was attached to the operating microscope with a custom adapter.Microscopic surgeon’s view and direct surgeon’s view through this new camera were recorded in the surgical recording system.Both movies were synchronized and analyzed how do surgeons handle the instruments.RESULTS:A small camera attached to the operating microscope allowed the surgeon’s hands motion to be recorded without interfering with the surgeon’s movements.Different surgeons used different methods to manipulate the ultrasound handpiece and the irrigation/aspiration device.Even in the simple paracentesis procedure,different surgeons used different methods.Surgeons-in-training were able to identify and improve their weaknesses by watching synchronized movies of their hand motions and microscopic view.CONCLUSION:Simultaneous recording the surgical field out of the operating microscopic view by a small camera set on the microscope is comprehensive and improves surgeons-in-training understanding and learning surgeries.

Mechanical response and microscopic damage mechanism of pre-flawed sandstone subjected to monotonic and multilevel cyclic loading:A laboratory-scale investigation

This study aims to investigate the mechanical response and acoustic emission(AE)characteristic of pre-flawed sandstone under both monotonic and multilevel constant-amplitude cyclic loads.Specifically,we explored how coplanar flaw angle and load type impact the strength and deformation behavior and microscopic damage mechanism.Results indicated that being fluctuated before rising with increasing fissure angle under monotonic loading,the peak strength of the specimen first increased slowly and then steeply under cyclic loading.The effect of multilevel cyclic loading on the mechanical parameters was more significant.For a single fatigue stage,the specimen underwent greater deformation in early cycles,which subsequently stabilized.Similar variation pattern was also reflected by AE count/energy/b-value.Crack behaviors were dominated by the fissure angle and load type and medium-scale crack accounted for 74.83%–86.44%of total crack.Compared with monotonic loading,crack distribution of specimen under cyclic loading was more complicated.Meanwhile,a simple model was proposed to describe the damage evolution of sandstone under cyclic loading.Finally,SEM images revealed that the microstructures at the fracture were mainly composed of intergranular fracture,and percentage of transgranular fracture jumped under cyclic loading due to the rapid release of elastic energy caused by high loading rate.

Single-factor analysis and interaction terms on the mechanical and microscopic properties of cemented aeolian sand backfill

The use of aeolian sand(AS)as an aggregate to prepare coal mine cemented filling materials can resolve the problems of gangue shortage and excessive AS deposits.Owing to the lack of research on the mechanism of cemented AS backfill(CASB),the response surface method(RSM)was adopted in this study to analyze the influence of ordinary Portland cement(PO)content(x_(1)),fly ash(FA)-AS(FA-AS)ratio(x_(2)),and concentration(x_(3))on the mechanical and microscopic properties of the CASB.The hydration characteristics and internal pore structure of the backfill were assessed through thermogravimetric/derivative thermogravimetric analysis,mercury intrusion porosimetry,and scanning electron microscopy.The RSM results show that the influence of each factor and interaction term on the response values is extremely significant(except x_(1)x_(3),which had no obvious effect on the 28 d strength).The uniaxial compressive strength(UCS)increased with the PO content,FA-AS ratio,and concentration.The interaction effects of x_(1)x_(2),x_(1)x_(3),and x_(2)x_(3) on the UCS at 3,7,and 28 d were analyzed.In terms of the influence of interaction items,an improvement in one factor promoted the strengthening effect of another factor.The enhancement mechanism of the curing time,PO content,and FA-AS ratio on the backfill was reflected in the increase in hydration products and pore structure optimization.By contrast,the enhancement mechanism of the concentration was mainly the pore structure optimization.The UCS was positively correlated with weight loss and micropore content but negatively correlated with the total porosity.The R^(2) value of the fitting function of the strength and weight loss,micropore content,and total porosity exceeded 0.9,which improved the characterization of the enhancement mechanism of the UCS based on the thermogravimetric analysis and pore structure.This work obtained that the influence rules and mechanisms of the PO,FA-AS,concentration,and interaction terms on the mechanical properties of the CASB provided a certain theoretical and engineering guidance for CASB filling.

Microscopic cracking behaviors of rocks under uniaxial compression with microscopic multiphase heterogeneity by deep learning

Cracking behaviors of rocks significantly affect the safety and stability of the explorations of underground space and deep resources.To understand deeply the microscopic cracking process and mechanical property of rocks,X-ray micro-computed tomography(X-μCT)is applied to capture the rock microstructures.The digital color difference UNet(DCD-UNet)-based deep learning algorithm with 3D reconstruction is proposed to reconstruct the multiphase heterogeneity microstructure models of rocks.The microscopic cracking and mechanical properties are studied based on the proposed microstructure-based peridynamic model.Results show that the DCD-UNet algorithm is more effective to recognize and to represent the microscopic multiphase heterogeneity of rocks.As damage characteristic index of multiphase rocks increases,transgranular cracks in the same grain phase,transgranular and intergranular cracks of pore-grain phase,intergranular and secondary transgranular cracks and transgranular crack between different grains propagate.The ultimate microscopic failure modes of rocks are mainly controlled by the transgranular cracks-based T1-shear,T3-shear,T1-tension,T2-tension and T3-tension failures,and the intergranular cracks-based T1-tension,T1-shear and T3-shear failures under uniaxial compression.

Efficient Origin-Destination Estimation Using Microscopic Traffic Simulation with Restricted Rerouting

Traffic simulators are utilized to solve a variety of traffic-related problems.For such simulators,origin-destination(OD)traffic volumes as mobility demands are required to input,and we need to estimate them.The authors regard an OD estimation as a bi-level programming problem,and apply a microscopic traffic simulation model to it.However,the simulation trials can be computationally expensive if full dynamic rerouting is allowed,when employing multi-agent-based models in the estimation process.This paper proposes an efficient OD estimation method using a multi-agent-based simulator with restricted dynamic rerouting to reduce the computational load.Even though,in the case of large traffic demand,the restriction on dynamic rerouting can result in heavier congestion.The authors resolve this problem by introducing constraints of the bi-level programming problem depending on link congestion.Test results show that the accuracy of the link traffic volume reproduced with the proposed method is virtually identical to that of existing methods but that the proposed method is more computationally efficient in a wide-range or high-demand context.

An image mosaic technique with non-overlapping regions based on microscopic vision in precision assembly

Microscopic vision has been widely applied in precision assembly.To achieve sufficiently high resolution in measurements for precision assembly when the sizes of the parts involved exceed the field of view of the vision system,an image mosaic technique must be used.In this paper,a method for constructing an image mosaic with non-overlapping areas with enhanced efficiency is proposed.First,an image mosaic model for the part is created using a geometric model of the measurement system installed on a X-Y-Z precision stages with high repeatability,and a path for image acquisition is established.Second,images are captured along the same path for a specified calibration plate,and an entire image is formed based on the given model.The measurement results obtained from the specified calibration plate are utilized to identify mosaic errors and apply compensation for the part requiring measurement.Experimental results show that the maximum error is less than 4μm for a camera with pixel equivalent 2.46μm,thereby demonstrating the accuracy of the proposed method.This image mosaic technique with non-overlapping regions can simplify image acquisition and reduce the workload involved in constructing an image mosaic.

Simulation analysis on microscopic discharge characteristics of the bipolar corona of a floating conductor

A floating conductor exhibits a bipolar corona phenomenon with microscopic discharge characteristics that are still unclear.In this study,a plasma simulation model of the bipolar corona with 108 chemical reaction equations is established by combining hydrodynamics and plasma chemical reactions.The evolution characteristics of electrons,positive ions,negative ions and neutral particles,as well as the distribution characteristics of space charges are analyzed,and the evolutionary flow of microscopic particles is summarized.The results indicate that the positive end of the bipolar corona initiates discharge before the negative end,but the plasma chemistry at the negative end is more vigorous.The electron generation rate can reach 1240 mol(m^(3) s)^(-1),and the dissipation rate can reach 34 mol(m^(3) s)^(-1).The positive ion swarm is dominated by O_(4)^(+),and the maximum generation rate can reach 440 mol((m^(3) s)^(-1).The negative ion swarm is mainly O_(2) and O_(4).The O_(2) content is approximately 1.5-3 times that of O_(4),and the maximum reaction rate can reach 51 mol(m^(3) s)^(-1).The final destination of neutral particles is an accumulation in the form of O_(3) and NO,and the amount of O3 produced is approximately 4-6 times that of NO.The positive end of the bipolar corona is dominated by positive space charges,which continue to develop and spread outwards in the form of a pulse wave.The negative end exhibits a space charge distribution structure of concentrated positive charges and diffused negative charges.The validity of the microscopic simulation analysis is verified by the macroscopic discharge phenomenon.

Stress sensitivity of carbonate gas reservoirs and its microscopic mechanism

In order to evaluate the stress sensitivity of carbonate reservoirs,a series of rock stress sensitivity tests were carried out under in-situ formation temperature and stress condition.Based on the calibration of capillary pressure curve,the variable fractal dimension was introduced to establish the conversion formula between relaxation time and pore size.By using the nuclear magnetic resonance(NMR)method,the pore volume loss caused by stress sensitivity within different scales of pore throat was quantitatively analyzed,and the microscopic mechanism of stress sensitivity of carbonate gas reservoirs was clarified.The results show that fractures can significantly affect the stress sensitivity of carbonate reservoirs.With the increase of initial permeability,the stress sensitivity coefficient decreases and then increases for porous reservoirs,but increases monotonously for fractured-porous reservoirs.The pore volume loss caused by stress sensitivity mainly occurs for mesopores(0.02–0.50μm),contributing more than 50%of the total volume loss.Single high-angle fracture contributes 9.6%of the stress sensitivity and 15.7%of the irreversible damage.The microscopic mechanism of the stress sensitivity of carbonate gas reservoirs can be concluded as fracture closure,elastic contraction of pores and plastic deformation of rock skeleton.

Spatial-Spectral Joint Network for Cholangiocarcinoma Microscopic Hyperspectral Image Classification

Accurate histopathology classification is a crucial factor in the diagnosis and treatment of Cholangiocarcinoma(CCA).Hyperspectral images(HSI)provide rich spectral information than ordinary RGB images,making them more useful for medical diagnosis.The Convolutional Neural Network(CNN)is commonly employed in hyperspectral image classification due to its remarkable capacity for feature extraction and image classification.However,many existing CNN-based HSI classification methods tend to ignore the importance of image spatial context information and the interdependence between spectral channels,leading to unsatisfied classification performance.Thus,to address these issues,this paper proposes a Spatial-Spectral Joint Network(SSJN)model for hyperspectral image classification that utilizes spatial self-attention and spectral feature extraction.The SSJN model is derived from the ResNet18 network and implemented with the non-local and Coordinate Attention(CA)modules,which extract long-range dependencies on image space and enhance spatial features through the Branch Attention(BA)module to emphasize the region of interest.Furthermore,the SSJN model employs Conv-LSTM modules to extract long-range depen-dencies in the image spectral domain.This addresses the gradient disappearance/explosion phenom-ena and enhances the model classification accuracy.The experimental results show that the pro-posed SSJN model is more efficient in leveraging the spatial and spectral information of hyperspec-tral images on multidimensional microspectral datasets of CCA,leading to higher classification accuracy,and may have useful references for medical diagnosis of CCA.

Subcutaneous pedicled propeller flap technique for microscopic reconstruction of eyelid defects

AIM:To describe the subcutaneous pedicled propeller flap technique for the microscopic reconstruction of eyelid defects and evaluate its outcomes.METHODS:The clinical data of 23 patients(23 eyes)who underwent microscopic reconstruction of eyelid defects with the subcutaneous pedicled propeller flap technique were retrospectively analyzed.All patients underwent eyelid tumor resection and one-stage microscopic reconstruction with the subcutaneous pedicled propeller flap for anterioror posterior-layer eyelid defects.The survival rate of the propeller flap,eyelid function and appearance,tumor recurrence rate,and patient satisfaction were evaluated after the surgery.RESULTS:The patients consisted of 12 men and 11 women,aged 31–82y(mean,58.9y).The longest followup time was 5y,and the shortest was 3mo.All the propeller flaps survived well.There was no significant difference in color and luster between the flap and adjacent tissues,and there was no dog ear phenomenon.No obvious scarring was observed.There were no obvious abnormalities of eyelid morphology or function,and no adverse complications such as exposure keratitis,entropion,ectropion,ptosis,and eyelid retraction.No tumor recurrence was found at the time of the last follow-up.All patients were satisfied with the surgical results.CONCLUSION:The subcutaneous pedicled propeller flap technique for the microscopic reconstruction of eyelid defects has satisfactor y outcomes in terms of eyelid function and esthetics,and merits clinical application.

Microscopic Characteristics and Routine Detection of Hedyotis hedyotidea(DC.)Merr.

[Objectives]To study the microscopic characteristics and routine detection of Hedyotis hedyotidea(DC.)Merr.[Methods]The microscopic characteristics of the root,stem cross section and the whole plant powder of H.hedyotidea were studied by the methods of slide-shaft section,biological staining and microscopic imaging;the routine detection items such as moisture,ash,acid-insoluble ash and extract were detected and analyzed in accordance with the requirements of Chinese Pharmacopoeia.[Results]The microscopic characteristics of the root,the stem and the whole plant powder of H.hedyotidea were obtained.The moisture content of 10 batches of H.hedyotidea samples was in the range of 4.25%-7.90%,the water-soluble extract is in the range of 15.08%-22.52%,the total ash was in the scope of 8.27%-10.45%,and the acid-insoluble ash was in 0.13%-0.95%.The proposed water content of H.hedyotidea should not exceed 10.00%,the water-soluble extract should not be less than 12.00%,the total ash content should not exceed 13.00%,and the acid-insoluble ash content should not exceed 1.20%.[Conclusions]The results of this experiment can provide a reference for the quality control and quality standard of H.hedyotidea.

Microscopic colitis: A review of etiology, treatment and refractory disease

Microscopic colitis is a common cause of chronic,nonbloody diarrhea. Microscopic colitis is more common in women than men and usually affects patients in their sixth and seventh decade. This article reviews the etiology and medical management of microscopic colitis. The etiology of microscopic colitis is unknown, but it is associated with autoimmune disorders, such as celiac disease, polyarthritis, and thyroid disorders. Smoking has been identified as a risk factor of mi-croscopic colitis. Exposure to medications, such as non-steroidal anti-inflammatory drugs, proton pump inhibitors, and selective serotonin reuptake inhibitors, is suspected to play a role in microscopic colitis, although their direct causal relationship has not been proven. Multiple medications, including corticosteroids, anti-diarrheals, cholestyramine, bismuth, 5-aminosalicylates, and immunomodulators, have been used to treat microscopic colitis with variable response rates. Budesonide is effective in inducing and maintaining clinical remission but relapse rate is as high as 82% when budesonide is discontinued. There is limited data on management of steroid-dependent microscopic colitis or refractory microscopic colitis. Immunomodulators seem to have low response rate 0%-56% for patients with refractory microscopic colitis. Response rate 66%-100% was observed for use of anti-tumor necrosis factor(TNF) therapy for refractory microscopic colitis. Anti-TNF and diverting ileostomy may be an option in severe or refractory microscopic colitis.