An IMPES scheme for a two-phase flow in heterogeneous porous media using a structured grid

Jo, Gwanghyun,Kwak, Do Y. Elsevier 2017 Computer methods in applied mechanics and engineer Vol.317 No.-

<P><B>Abstract</B></P> <P>We develop a numerical scheme for a two-phase immiscible flow in heterogeneous porous media using a structured grid finite element method, which has been successfully used for the computation of various physical applications involving elliptic interface equations (Li et al., 2003, 2004; Chou et al., 2010; Kwak et al., 2010; Chang and Kwak, 2011). The proposed method is based on the implicit pressure-explicit saturation procedure. To solve the pressure equation, we use an IFEM based on the Rannacher–Turek Rannacher and Turek (1992) nonconforming space, which is a modification of the work in Kwak et al. (2010) where ‘broken’ <SUB> P 1 </SUB> nonconforming element of Crouzeix–Raviart (1973) was developed.</P> <P>For the Darcy velocity, we apply the mixed finite volume method studied in Chou et al. (2003) and Kwak et al. (2010) on the basis of immersed finite element method (IFEM). In this way, the Darcy velocity of the flow can be computed cheaply (locally) after we solve the pressure equation. The computed Darcy velocity is used to solve the saturation equation explicitly. The whole procedure can be implemented on a structured grid which is independent of the underlying heterogeneous porous media. In fact, we apply a new version of multigrid algorithm to solve the pressure equation for which the CPU time grows like O ( N ) . Numerical tests for analytic problems show that our method is almost optimal in all variables. Problem with sources/sinks is also computed and it seems to work well.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We develop a numerical scheme for a two-phase flow in heterogeneous porous media. </LI> <LI> We use an IFEM for pressure and MFVM for Darcy velocity. </LI> <LI> We apply a multigrid algorithm to the pressure equation and compare with a PCG. </LI> <LI> Numerical results show that our method exhibits optimal order convergence. </LI> <LI> CPU time of our multigrid algorithm grows linearly as the level increases. </LI> </UL> </P>

Neural Network Based Simulation of Poisson Boltzmann Equation

Gwanghyun Jo(조광현),Kwang-Seong Shin(신광성) 한국정보통신학회 2021 한국정보통신학회 종합학술대회 논문집 Vol.25 No.2

본 논문에서 뉴럴 네트워크를 활용하여 포아즌 볼츠만 방정식을 푸는 방법을 소개하려 한다. 기존의 유한요소방법을 사용하여 샘플을 생성하고, 생성된 샘플을 이용하여 뉴럴 네트워크를 훈련시킨다. 결과적으로 얻어진 뉴럴 네트워크의 성능을 소개한다. This work introduces neural network based simulation for Poisson Boltzmann equation. First, samples are generated via a finite element method, whose pairs are used to train neural network. We report the performance of the neural network.

[P250] Onychomatricoma manifesting longitudinal melanonychia

( Gwanghyun Jo ),( Je-ho Mun ) 대한피부과학회 2017 대한피부과학회 학술발표대회집 Vol.69 No.1

Onychomatricoma is a rare benign fibroepithelial tumor of the nail unit. It usually presents as yellowish longitudinal bands, splinter hemorrhages, and overcurvature of the nailplate. Although it is rare, it can take the form of longitudinal melanonychia. Therefore, differential diagnosis with nail unit melanoma is necessary. A 67-year-old man presented with an 8-month history of gray longitudinal melanonychia on the medial aspect of the left first toe. He was under treatment with chemotherapy for non-small-cell lung cancer with metastasis to the pericardium. Physical examination showed longitudinal gray bands with longitudinal ridging. Because it had occurred recently, we performed a biopsy to rule out malignant melanoma. After partial nail plate avulsion, a villous tumor of the nail matrix which penetrated the thickened nail plate was shown. Surgical excision of the tumor was performed, after whichhistopathologic examination revealed papillomatous fibroepithelial tumor. Spindle cell proliferation with occasional mast cells was observed in the stroma of the tumor. Immunohistochemical staining showed that CD10 and CD34 were expressed in the stroma of the tumor. Grocott’s methenamine silver and Periodic acid-Schiff staining of avulsed nail plate were negative for fungi, leading to a diagnosis of onychomatricoma based on the findings. We report here a rare case of onychomatricoma presenting as melanonychia striata.

[P203] Erosive adenomatosis of the nipple in a young man with HIV infection

( Gwanghyun Jo ),( Je-ho Mun ) 대한피부과학회 2017 대한피부과학회 학술발표대회집 Vol.69 No.1

Erosive adenomatosis of the nipple (EAN), also known as nipple adenoma, is a rare benign neoplasm of the nipple duct. It usually occurs in women, and cases of EAN in men are extremely rare. Recently, we experienced a case of EAN in a young man with human immunodeficiency virus (HIV) infection. To our knowledge, there has been no report of EAN in a HIV patient in the literature. A 21-year-old, HIV-infected man who had been receiving antiviral medication, presented with a 4-year history of ulcerative change on the left nipple with reports of occasional pain. Laboratory tests revealed high HIV viral load and low CD4 count. The lesion did not show any improvement in topical steroid treatment for 2 weeks. Therefore, differential diagnosis with mammary Paget``s disease was necessary. A punch biopsy of the lesion showed a proliferation of gland-like or tubular structures in the dermis. The tubular structures were lined by flat myoepithelial cells and cuboidal epithelial cells with decapitation secretion. There was no nuclear atypia. Based on the histopathologic findings, we diagnosed this lesion as EAN. Surgical excision of the involved nipple was performed. The patient is doing well without recurrence one year after surgery. Although the association between HIV-infection and glandular proliferative disease of the breast has been reported, this occurrence of EAN in HIV-infection patients is the first to be reported in the literature.

[P287] Altered mentality in a patient with herpes zoster

( Gwanghyun Jo ),( Hyun-sun Yoon ),( Soyun Cho ),( Hyunsun Park ) 대한피부과학회 2017 대한피부과학회 학술발표대회집 Vol.69 No.1

A 70-year-old woman who was treated for herpes zoster presented with confusion. Physical examination, laboratory tests, cerebrospinal fluid (CSF) analysis, and computed tomography of the brain were performed. She was diagnosed as zoster encephalitis (ZE) with syndrome of inappropriate secretion of antidiuretic hormone (SIADH). After the correction of electrolyte imbalance and antiviral treatment for 2 weeks, she almost recovered to normal. When mental alteration occurs in herpes zoster patients, ZE or SIADH should be suspected. Immunocompromised states such as old age, diabetes mellitus, transplantation, malignancy and acquired immunodeficiency syndrome are risk factors for both ZE and SIADH. ZE manifest diverse conditions such as ischemic and hemorrhagic infarctions, demyelinating disease, seizures, and mental status changes. Such conditions in herpes zoster patients with the absence of other causes could be diagnosed with ZE. Detection of varicella-zoster virus by polymerase chain reaction of CSF is diagnostic. SIADH accompanied by herpes zoster is well documented. The mechanism is not clear. Hypo-osmolar euvolemic hyponatremia with elevated urine osmolality and Na+ concentration without cardiac, renal, hepatic, and endocrine dysfunction are consistent with the diagnosis of SIADH. Here we report this case for dermatologists to know the causes of mental alteration in immunocompromised herpes zoster patients and to cope well with them.

Squamous cell carcinoma of the nail unit: a retrospective review of 17 cases and our proposal for surgical management

( Gwanghyun Jo ),( Tae Min Lee ),( Soo Ick Cho ),( Seong-jin Jo ),( Kwang-hyun Cho ),( Je-ho Mun ) 대한피부과학회 2017 대한피부과학회 학술발표대회집 Vol.69 No.2

Background: Reports regarding nail unit squamous cell carcinoma (NUSCC) are rare in Asia Objectives: To investigate clinical and histopathological characteristics of NUSCC in our institution and to propose a management algorithm. Methods: We performed a retrospective analysis of patients with NUSCC at Seoul National University Hospital over a period of 5 years (from April 2012 to April 2017) and literature review regarding NUSCC. Results: Seventeen cases were included. Eleven patients were male (64.7%). The fingers were more frequently affected (76.5%). Median duration of the disease at diagnosis was 3 years (Range: 0.3-22 years). The misdiagnosis rate was high (82.4%). The frequent clinical signs were subungual nodules, ulcer, nail dystrophy, and subungual hyperkeratosis. Most of the cases were invasive (76.5%). In terms of surgical methods, local excision, en-bloc excision of the nail unit, Mohs micrographic surgery, and digital amputation were performed on 23.5%, 11.8%, 35.3%, and 29.4% of the patients, respectively. Distant metastasis was not detected in all cases; however, recurrence was found in 2 cases (11.7%). Conclusion: Misdiagnosis of NUSCC was common, and most of the cases had prolonged delays until correct diagnosis was established. The majority of the lesions were invasive. Based on our surgical experience and literature review, we propose an algorithm for management of NUSCC depending on the proportion of nail involvement, the presence of dermal invasion, and bone involvement.

Dermoscopy of trachyonychia: a comparative study with onychomycosis

( Gwanghyun Jo ),( Jungyoon Ohn ),( Je-ho Mun ) 대한피부과학회 2017 대한피부과학회 학술발표대회집 Vol.69 No.2

Background: Diagnosing trachyonychia is often challenging and misdiagnosis as onychomycosis is common. Dermoscopy is a useful tool in various nail disorders. However, there are limited data regarding dermoscopic features of trachyonychia. Objectives: To characterize the dermoscopic features of trachyonychia and to investigate whether they are helpful in the differential diagnosis from onychomycosis. Methods: We evaluated the dermoscopic features of trachyonychia diagnosed at a tertiary referral center in Seoul, Korea from July 2015 to June 2017. We included onychomycosis as a control group for comparison. Results: Thirty trachyonychia and the same number of onychomycosis cases were analyzed. Statistical analysis revealed that longitudinal ridging, affected width > 50%, proximal involvement, thickened and ragged cuticle, lunular loss, splinter hemorrhage, pitting, red color, and onychoschizia were more common in trachyonychia. However, distal streak, subungual hyperkeratosis, and onycholysis were less frequent in trachyonychia than in onychomycosis. Conclusion: This study revealed distinctive dermoscopic features of trachyonychia. Therefore, dermoscopy can be used as a helpful tool for diagnosing trachyonychia.

[P473] A case of pembrolizumab induced lichen planus like drug eruptions

( Gwanghyun Jo ),( Chong Won Choi ),( Seong-jin Jo ),( Kwang-hyun Cho ) 대한피부과학회 2017 대한피부과학회 학술발표대회집 Vol.69 No.1

New advances in immunology have highlighted the role of the programmed cell death (PD)-1 protein in the suppression of the immune system. The use of recently-introduced anti-PD1 antibodies is rapidly increasing to combat cancer; they can activate the anti-cancer immune response by reversing the PD-1-induced inhibition of the immune system and thus control the progression of tumor cells. Pembrolizumab is a humanized anti-PD1 antibody approved for the treatment of unresectable or metastatic melanoma following disease progression after the treatment of ipilimumab. The adverse effects of pembrolizumab include pneumonitis, colitis, hepatitis and endocrinopathies, some of which may be related to the immunoregulatory mechanisms of the drug. In addition, several cutaneous adverse events have also been reported in association with the drug. Here we describe a case of lichen planus-like drug eruption following pembrolizumab treatment. A 72-year-old man underwent pembrolizumab treatment for small cell lung cancer. After ten courses of the treatment, he developed skin rashes, for which he was referred to our department for evaluation. The itchy, round erythematous plaques were found on his upper and lower extremities. Histopathologic examination revealed interface dermatitis with a few apoptotic keratinocytes in the basal layer. Thus, he was diagnosed with pembrolizumab-induced lichen planus-like drug eruption and treated with topical steroids.

Enriched P1-Conforming Methods for Elliptic Interface Problems with Implicit Jump Conditions

Jo, Gwanghyun,Kwak, Do Y. Hindawi Limited 2018 Advances in mathematical physics Vol.2018 No.-

<P>We develop a numerical method for elliptic interface problems with implicit jumps. To handle the discontinuity, we enrich usual <TEX>$ P_{\mathrm{1}}$</TEX> -conforming finite element space by adding extra degrees of freedom on one side of the interface. Next, we define a new bilinear form, which incorporates the implicit jump conditions. We show that the bilinear form is coercive and bounded if the penalty term is sufficiently large. We prove the optimal error estimates in both energy-like norm and <TEX>$ L^{\mathrm{2}}$</TEX> -norm. We provide numerical experiments. We observe that our scheme converges with optimal rates, which coincides with our error analysis.</P>

RECENT DEVELOPMENT OF IMMERSED FEM FOR ELLIPTIC AND ELASTIC INTERFACE PROBLEMS

GWANGHYUN JO,DO YOUNG KWAK 한국산업응용수학회 2019 Journal of the Korean Society for Industrial and A Vol.23 No.2

We survey a recently developed immersed finite element method (IFEM) for the interface problems. The IFEM uses structured grids such as uniform grids, even if the interface is a smooth curve. Instead of fitting the curved interface, the bases are modified so that they satisfy the jump conditions along the interface. The early versions of IFEM [1, 2] were suboptimal in convergence order [3]. Later, the consistency terms were added to the bilinear forms [4, 5], thus the scheme became optimal and the error estimates were proven. For elasticity problems with interfaces, we modify the Crouzeix-Raviart based element to satisfy the traction conditions along the interface [6], but the consistency terms are not needed. To satisfy the Korn’s inequality, we add the stabilizing terms to the bilinear form. The optimal error estimate was shown for a triangular grid. Lastly, we describe the multigrid algorithms for the discretized system arising from IFEM. The prolongation operators are designed so that the prolongated function satisfy the flux continuity condition along the interface. The W-cycle convergence was proved, and the number of V-cycle is independent of the mesh size.