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Purpose Detection of hidden defects of aluminum alloy plate with damping coating is a challenging problem. At present, only a few non-destructive testing methods exist to address this engineering problem. Without the restriction of skin effect, remote field eddy current (RFEC) overcomes the interference caused by the damping coating. The RFEC, which has potential advantages for detecting the hidden defects of aluminum plate with damping coating, can penetrate the metal plate to detect buried depth defects. This study aims to test how thick the RFEC sensor can penetrate the metal plate to detect the buried defects. Design/methodology/approach The magnetic field distribution characteristics are analyzed, the magnetic field intensity distribution is calculated, and the structure and parameters of the coil, magnetic circuit and shielding damping are determined through the two- and three-dimensional finite element simulation methods. Optimal excitation frequency is obtained, and the distance between the excitation coil and detection coil is determined by analyzing the relationship between excitation frequency and remote field points. Findings Simulation and experimental results verify the feasibility of applying the RFEC detection technology in detecting the hidden defects of aluminum alloy plate with damping coating. Originality/value In this paper, the RFEC testing model of hidden defects in aluminum plate sample with damping coating is established by using the finite element method.

Grade 3, type 3 gastric neuroendocrine tumor (g-NET) shows specific features of clinical interest and the therapeutic management of the lesion is not yet completely standardized. We present the unusual case of a 34-year-old male patient with a diminutive (less than 0.5 cm), well-differentiated, G3, type 3g-NET with extremely high Ki-67 index (higher than 80%). The lesion was subsequently removed en bloc via endoscopic submucosal dissection. Regarding the proliferation rate, Ki-67 index values usually range from 21 to 50%, and less commonly above 55%, in G3 NET. To our knowledge, this lesion represents a small size with the highest Ki-67 index diagnosed with G3 g-NET. However, as g-NET might recur even after a long duration, we recommend a long-term follow-up, such as 10 years after complete resection in patients to evaluate the endoscopic resection approach.

PD-L1+ tumor-derived extracellular vesicles (TEVs) cause systemic immunosuppression and possibly resistance to anti-PD-L1 antibody (αPD-L1) blockade. However, whether and how PD-L1+ TEVs mediate αPD-L1 therapy resistance is unknown. Here, we show that PD-L1+ TEVs substantially decoy αPD-L1 and that TEV-bound αPD-L1 is more rapidly cleared by macrophages, causing insufficient blockade of tumor PD-L1 and subsequent αPD-L1 therapy resistance. Inhibition of endogenous production of TEVs by Rab27a or Coro1a knockout reverses αPD-L1 therapy resistance. Either an increased αPD-L1 dose or macrophage depletion mediated by the clinical drug pexidartinib abolishes αPD-L1 therapy resistance. Moreover, in the treatment cycle with the same total treatment dose of αPD-L1, high-dose and low-frequency treatment had better antitumor effects than low-dose and high-frequency treatment, induced stronger antitumor immune memory, and eliminated αPD-L1 therapy resistance. Notably, in humanized immune system mice with human xenograft tumors, both increased αPD-L1 dose and high-dose and low-frequency treatment enhanced the antitumor effects of αPD-L1. Furthermore, increased doses of αPD-L1 and αPD-1 had comparable antitumor effects, but αPD-L1 amplified fewer PD-1+ Treg cells, which are responsible for tumor hyperprogression. Altogether, our results reveal a TEV-mediated mechanism of αPD-L1-specific therapy resistance, thus providing promising strategies to improve αPD-L1 efficacy.

Background The risk for gastric cancer among patients with gastric atrophy is unclear. We investigated the association between the risk for gastric cancer and gastric atrophy. Methods We performed a comprehensive literature search in the PubMed and Embase databases and extracted relevant data from eligible studies. A fixed- or random-effects model was applied to pool study-specific risk according to heterogeneity across studies. Results Thirteen cohort or nested case-control studies with 655,937 participants and 2,794 patients with gastric cancer were analyzed. The pooled results suggested that gastric atrophy was associated with an elevated risk for gastric cancer [pooled risk ratio (RR) =2.91, 95% confidence interval (CI): 2.58–3.27]. The pooled RR (3.10, 95% CI: 2.58–3.73) of studies that used serum levels of pepsinogen for diagnosis of gastric atrophy was similar to that of those that used (pooled RR =2.79, 95% CI: 2.37–3.27) (for endoscopy). Gastric atrophy was positively associated with the risk for gastric cancer in both prospective and retrospective studies. Moreover, the pooled RRs did not significantly vary by country of origin (Asia and Europe) or gastric cancer subtype (cardia and non-cardia). Conclusions Gastric atrophy is associated with an elevated risk for gastric cancer, and endoscopy and serum levels of pepsinogens can be used to predict the risk.

This study aimed to compare the radiologic size of gastric gastrointestinal stromal tumors (GISTs) on computed tomography (CT) with the pathologic size in a Chinese population, and elucidate the potential significance of the CT size in the preoperative risk stratification.The study enrolled 314 patients treated by endoscopic/surgical resection of gastric lesions that proved postoperatively to be GISTs. Bland-Altman analysis and intraclass correlation coefficient (ICC) were adopted to assess the size agreement between CT and pathology. Independent predictors of risk category underestimation and the optimal cut-off value of CT size were determined by logistic regression analysis and the receiver operating characteristic (ROC) curve.CT underestimated gastric GISTs size by 0.30 cm [95% confidence interval (CI): (-0.42, - 0.19); p lt; 0.001]. In the subgroup analysis, the size underestimation was 0.10 cm in GISTs ≤ 5 cm [95% CI: (-0.19, -0.01); p = 0.024]; and 0.75 cm in GISTsgt;5 cm [95% CI: (-1.05, 0.45), p lt; 0.001]. Though ICC values showed well reliability for the corresponding pathologic size, with 0.95 in all size, 0.86 in size ≤ 5 cm, and 0.92 in sizegt;5 cm respectively. Risk underestimation by CT imaging mainly occurred in gastric GISTs with smaller size (≤5 cm; p = 0.010) and lower mitotic index (≤5 per 50 high-power fields; p = 0.011). CT size of 3.65 cm was defined as an absolute cut-off to differentiate intermediate/high-risk patients from low-risk group, with 87.5% sensitivity at a specificity of 57.8%.Preoperative CT underestimated the mean size by 0.30 cm in gastric GISTs. A CT size of 3.65 cm would facilitate the selection of potential intermediate/high-risk patients, instant intervention should be encouraged in the absence of contraindications.

Multivesicular bodies (MVBs) fuse with not only the plasma membranes to release extracellular vesicles (EVs) but also lysosomes for degradation. Rab7 participates in the lysosomal targeting of MVBs. However, the proteins on MVB that directly bind Rab7, causing MVB recruitment of Rab7 remain unidentified. Here, we show that Coro1a undergoes neddylation modification at K233 by TRIM4. Neddylated Coro1a is associated with the MVB membrane and facilitates MVB recruitment and activation of Rab7 by directly binding Rab7. Subsequently, MVBs are targeted to lysosomes for degradation in a Rab7‐dependent manner, leading to reduced EV secretion. Furthermore, a decrease in neddylated Coro1a enhances the production of tumour EVs, thereby promoting tumour progression, indicating that neddylated Coro1a is an ideal target for the regulation of EV biogenesis. Altogether, our data identify a novel substrate of neddylation and reveal an unknown mechanism for MVB recruitment of Rab7, thus providing new insight into the regulation of EV biogenesis.

Mutations in the APP gene are popularly known as the second cause trigger the familial Alzheimer's disease (AD). We generated a human induced pluripotent stem cell (iPSC) line from the peripheral blood mononuclear cells isolated from an AD patient using non-integrative Sendai virus. The iPSC line highly expresses pluripotency markers, has the capacity to differentiate into the normal teratoma tissue, retains the APP mutation, and displays the normal karyotype. The iPSC line will provide a useful resource to study the pathogenesis and drugs screening of AD.

A family history of colorectal cancer (CRC) increases the risk of developing CRC, and numerous studies have assessed the influence of family history on survival among CRC patients. However, the prognostic effect of a family history of CRC remains uncertain. The aim of this meta-analysis was to systematically assess the association between family history and CRC prognosis.A comprehensive literature search was performed in the PubMed, Embase, Medline, Web of Science and Scopus databases up to October 2021, based on the Population, Intervention, Comparator, Outcomes and Study designs framework. Two reviewers independently extracted data on baseline characteristics and outcomes from the included studies. The Newcastle-Ottawa Scale was used for quality assessment of each study. Either a fixed- or a random-effects model was used to calculate the pooled hazard ratio (HR).Eighteen studies comprising 80,093 CRC patients were finally included in this meta-analysis. The Newcastle-Ottawa Scale scores of the included studies ranged from 4 to 8, and 12 studies were of high quality. A significant association between family history and improved overall survival was determined in the CRC patients (HR =0.89, 95% CI: 0.81-0.99) with significant heterogeneity (IIn conclusion, a positive family history was associated with improved overall survival in CRC patients. It was also a favorable predictor of disease-free survival in patients with stage III CRC. These findings should be interpreted with caution because of limitations related to study quality and differences in the adjusted factors across studies.

The origin and characteristics of most submucosal tumors (SMTs) cannot easily be confirmed by gastrointestinal endoscopy or other radiological examinations. Excluding GISTs, for those other gastric SMTs, most of which are deemed benign, the necessity and timing of intervention has been ignored. Thus, the malignancy of gastric SMTs still remains unknown. In order to summarize the malignancy of these gastric SMTs, we reviewed literatures and analyzed cases of gastric SMTs including heterotopic pancreas, leiomyoma, schwannoma, glomus tumor, hemangioendothelioma, granular cell tumor (GCT), lipoma, hemangiopericytoma, lymphangioma and neurofibroma. In these literatures, there are cases of malignancy among heterotopic pancreas, leiomyoma, schwannoma, glomus tumor, hemangioendothelioma and GCT. As a result, it suggests that although most of gastric SMTs are considered benign, there are still possibilities of malignancy, which requires our attention, even active intervention and long-term follow-up.

In view of the electro-hydraulic position servo system with parameter uncertainty and bounded disturbances, an improved adaptive sliding mode control scheme is proposed. The mathematical model of the valve-controlled system is first constructed with consideration of the external disturbance, matched and mismatched unknown parameters. Then, the parametric adaptive estimation laws are established by Lyapunov technique to estimate the generalized uncertainty parameters, and the discontinuous projection algorithm is used to ensure the boundedness of parameter estimation. In order to eliminate the chattering phenomenon in sliding mode control, the saturation function is designed to replace the sign function and the gain coefficient is adjustable on the sliding surface. Finally, the comparative experimental results clarify that the proposed control scheme has better control performance than the PID controller and the SMC controller.

Fas induces apoptosis in activated T cell to maintain immune homeostasis, but the effects of non-apoptotic Fas signaling on T cells remain unclear. Here we show that Fas promotes TH9 cell differentiation by activating NF-κB via Ca2+-dependent PKC-β activation. In addition, PKC-β also phosphorylates p38 to inactivate NFAT1 and reduce NFAT1-NF-κB synergy to promote the Fas-induced TH9 transcription program. Fas ligation exacerbates inflammatory bowel disease by increasing TH9 cell differentiation, and promotes antitumor activity in p38 inhibitor-treated TH9 cells. Furthermore, low-dose p38 inhibitor suppresses tumor growth without inducing systemic adverse effects. In patients with tumor, relatively high TH9 cell numbers are associated with good prognosis. Our study thus implicates Fas in CD4+ T cells as a target for inflammatory bowel disease therapy. Furthermore, simultaneous Fas ligation and low-dose p38 inhibition may be an effective approach for TH9 cell induction and cancer therapy.

Tumor progression depends on the collaborative interactions between tumor cells and the surrounding stroma. First-line therapies direct against cancer cells may not reach a satisfactory outcome, such as gastric cancer (GC), with high risk of recurrence and metastasis. Therefore, novel treatments and drugs target the effects of stroma components are to be promising alternatives. Mesenchymal stem cells (MSC) represent the decisive components of tumor stroma that are found to strongly affect GC development and progression. MSC from bone marrow or adjacent normal tissues express homing profiles in timely response to GC-related inflammation signals and anchor into tumor bulks. Then the newly recruited “naïve” MSC would achieve phenotype and functional alternations and adopt the greater tumor-supporting potential under the reprogramming of GC cells. Conversely, both new-comers and tumor-resident MSC are able to modulate the tumor biology via aberrant activation of oncogenic signals, metabolic reprogramming and epithelial-to-mesenchymal transition. And they also engage in remodeling the stroma better suited for tumor progression through immunosuppression, pro-angiogenesis, as well as extracellular matrix reshaping. On the account of tumor tropism, MSC could be engineered to assist earlier diagnosis of GC and deliver tumor-killing agents precisely to the tumor microenvironment. Meanwhile, intercepting and abrogating vicious signals derived from MSC are of certain significance for the combat of GC. In this review, we mainly summarize current advances concerning the reciprocal metabolic interactions between MSC and GC and their underlying therapeutic implications in the future.

We aimed to assess the association between allergic conditions and risk/mortality of colorectal cancer (CRC). A systematic literature search was conducted using Pubmed and Embase to identify relevant studies. Prospective studies assessing the association between allergic conditions and risk/mortality of CRC were included. Risk ratios (RRs) were pooled with either a fixed- or a random-effects model according to heterogeneity. A total of 515379 participants and 10345 CRC cases from 12 studies were included in the analysis of CRC risk, while four studies with 1484741 individuals and 30040 CRC deaths were included in the analysis of CRC mortality. The pooled RR for the association between allergic conditions and CRC risk was 0.88 (95% CI 0.83–0.92). The inverse association was observed both in colon cancer (pooled RR = 0.83, 95% CI 0.72–0.97) and rectal cancer (pooled RR = 0.83, 95% CI 0.74–0.93). Moreover, no gender difference was observed in the analysis of CRC risk (for males, pooled RR = 0.88, 95% CI 0.81–0.96; for females, pooled RR = 0.88, 95% CI 0.82–0.95). And allergic conditions were also found to be inversely associated with CRC mortality (pooled RR = 0.88, 95% CI 0.83–0.92). In conclusion, the current meta-analysis provides further evidence that allergic conditions were inversely associated with CRC risk and mortality.

Esophageal candidiasis (EC) is the most common type of infectious esophagitis. In the gastrointestinal tract, the esophagus is the second most susceptible to candida infection, only after the oropharynx. Immunocompromised patients are most at risk, including patients with HIV/AIDS, leukemia, diabetics, and those who are receiving corticosteroids, radiation, and chemotherapy. Another group includes those who used antibiotics frequently and those who have esophageal motility disorder (cardiac achalasia and scleroderma). Patients complained of pain on swallowing, difficulty swallowing, and pain behind the sternum. On physical examination, there is a plaque that often occurs together with oral thrush. Endoscopic examination is the best approach to diagnose this disease by directly observing the white mucosal plaque-like lesions and exudates adherent to the mucosa. These adherent lesions cannot be washed off with water from irrigation. This disease is confirmed histologically by taking the biopsy or brushings of yeast and pseudohyphae invading mucosal cells. The treatment is by systemic antifungal drugs given orally in a defined course. It is important to differentiate esophageal candidiasis from other forms of infectious esophagitis such as cytomegalovirus, herpes simplex virus, gastroesophageal reflux disease, medication-induced esophagitis, radiation-induced esophageal injury, and inflammatory conditions such as eosinophilic esophagitis. Except for a few complications such as necrotizing esophageal candidiasis, fistula, and sepsis, the prognosis of esophageal candidiasis has been good.

Early diagnosis is the key to improve the prognosis of gastric cancer. How to screen out high-risk subjects of gastric cancer in population is a hot spot. Serum-based early detection of gastric cancer is suitable for high-risk population screening, which is more convenient and safer. This article reviews the diagnostic value of serum biomarkers for gastric cancer, including serum DNA methylation, various RNAs, pepsinogen, gastrin, osteopontin, MG7-Ag and CA724. Until now, there is still lack of ideal biomarkers for gastric cancer, and searching for specific RNAs may be promising for early diagnosis and screening of gastric cancer.

In this paper, the dynamics of an electrohydraulic servo system is analyzed. It is difficult to achieve the precise force tracking control due to its high nonlinearities and parameter uncertainties. For the accurate force tracking control, a sliding mode control algorithm with radial basis function (RBF) neural network compensation was proposed. The theory verifies that the algorithm is globally asymptotically stable. The experimental results show that the proposed algorithm is not only effective and better than the PID control in the force tracking control, but also robust to external uncertain disturbances. DOI: http://dx.doi.org/10.5755/j01.mech.25.1.21279

Fas induces apoptosis in activated T cell to maintain immune homeostasis, but the effects of non-apoptotic Fas signaling on T cells remain unclear. Here we show that Fas promotes TH9 cell differentiation by activating NF-κB via Ca2+-dependent PKC-β activation. In addition, PKC-β also phosphorylates p38 to inactivate NFAT1 and reduce NFAT1-NF-κB synergy to promote the Fas-induced TH9 transcription program. Fas ligation exacerbates inflammatory bowel disease by increasing TH9 cell differentiation, and promotes antitumor activity in p38 inhibitor-treated TH9 cells. Furthermore, low-dose p38 inhibitor suppresses tumor growth without inducing systemic adverse effects. In patients with tumor, relatively high TH9 cell numbers are associated with good prognosis. Our study thus implicates Fas in CD4+ T cells as a target for inflammatory bowel disease therapy. Furthermore, simultaneous Fas ligation and low-dose p38 inhibition may be an effective approach for TH9 cell induction and cancer therapy., Fas signalling induces apoptosis of activated T cells to maintain immune homeostasis. Here the authors show that Fas also induces PKC-β activation to promote NF-κB-mediated TH9 cell differentiation, while p38 activation by PKC-β antagonizes this effect, thereby supporting a synergy between p38 inhibitor and Fas for TH9 differentiation.

This paper presents a power assist lower extremity exoskeleton and a fuzzy sliding mode compensation controller. First, the mechanical design of this exoskeleton and the control configuration are introduced. Second, the dynamics of lower extremity exoskeleton is analyzed and the sliding mode controller with fuzzy compensation algorithm under uncertainties for exoskeleton joints is proposed. The theoretical proof shows that it is globally stable in the sense of Lyapunov. The experiments indicate that the proposed control scheme is effective; not only it ensures the control accuracy but also is robust to external uncertainties compared with PID control. DOI: http://dx.doi.org/10.5755/j01.mech.24.1.14564

Plenty of studies have assessed the association between intestinal metaplasia (IM) and gastric cancer risk, while the results were inconsistent. We aimed to assess the risk of gastric cancer among patients with IM. Systematic literature searches were conducted in PubMed, Embase and Cochrane databases. Baseline characteristics and outcomes from the included studies were extracted independently by two investigators. Either a fixed-effects or a random-effects model was used to composite the pooled OR for gastric cancer risk. Finally, a total of 21 studies, which comprised 402,636 participants and 4,535 gastric cancer patients, were finally included in the current meta-analysis. Compared with those participants without IM, IM patients were at a higher risk of gastric cancer (pooled OR = 3.58, 95% CI 2.71-4.73). We observed that incomplete IM (pooled OR = 9.48, 95% CI 4.33-20.78) but not complete IM (pooled OR = 1.55, 95% CI 0.91-2.65) was significantly associated with a higher gastric cancer risk. Besides, it appeared that gastric cancer risk was higher among patients with IM in the corpus (pooled OR = 7.39, 95% CI 4.94-11.06) than those with IM in the antrum only (pooled OR = 4.06, 95% CI 2.79-5.91). And the pooled ORs for gastric noncardia cancer and gastric cardia cancer were 4.98 (95% CI 3.12-7.95) and 1.93 (95% CI 1.15-3.24), respectively. In conclusion, patients with IM were at a higher risk of gastric cancer, especially for incomplete IM and IM in the corpus. The current evidence supports the use of IM subtypes in the surveillance of gastric cancer.

Emerging 3D transistor structures and continued scaling requires conformal metal gate options with low resistivity, band edge work function and improved barrier properties. Doping ALD TiN with Si improves barrier properties shown with 10X reduced gate leakage. Both valence and conduction band edge work function can be met with low resistivity conformal films. The combination of ALD TiN, CVD Co and CVD Al can be used for low resistivity replacement metal gate fill for sub-15nm trenches.

Hepatic fibrosis is defined as a pathological process, and activation of hepatic stellate cells (HSCs) is believed to be the key event of liver fibrosis. Additionally, activated HSCs may participate in the formation of the tumor microenvironment. Polaprezinc, a protector of the gastric mucosa, has been recently demonstrated to be an inhibitor of liver fibrosis in a mouse model. Proliferation and colony formation assays were performed to determine the inhibitory effects of polaprezinc on the growth of LX‑2 and hepG2 cells. A migration assay was used to evaluate the change in mobility of LX‑2 cells and quantitative polymerase chain reaction was performed to detect the expression levels of key markers of fibrosis. Finally, a gene chip assay for polaprezinc‑treated hepG2 cells was performed to evaluate the effect of polaprezinc on the hepG2 gene expression profile. The proliferation assay indicated that polaprezinc may inhibit the LX‑2 cell proliferation and the migration assays confirmed the inhibition of mobility. The expression levels of fibrotic markers such as collagen I, fibronectin and α‑smooth muscle actin were downregulated following polaprezinc treatment. The proliferation activity of polaprezinc‑treated hepG2 cells was reduced and the gene chip assay indicated that series of gene expression changes associated with cancer migration, cell skeletal organization and proliferation had occurred. In conclusion, polaprezinc treatment mayinhibit the proliferation of hepatocellular carcinoma cells and reverse liver fibrosis by deactivating HSCs. The present findings suggest that polaprezinc provides a novel treatment for patients with gastritis complicated with cirrhosis.

Inflammation is frequently associated with initiation, progression, and metastasis of colorectal cancer (CRC). Here, we unveil a CRC-specific metastatic programme that is triggered via the transcriptional repressor, GFI1. Using data from a large cohort of clinical samples including inflammatory bowel disease and CRC, and a cellular model of CRC progression mediated by cross-talk between the cancer cell and the inflammatory microenvironment, we identified GFI1 as a gating regulator responsible for a constitutively activated signalling circuit that renders CRC cells competent for metastatic spread. Further analysis of mouse models with metastatic CRC and human clinical specimens reinforced the influence of GFI1 downregulation in promoting CRC metastatic spread. The novel role of GFI1 is uncovered for the first time in a human solid tumour such as CRC. Our results imply that GFI1 is a potential therapeutic target for interfering with inflammation-induced CRC progression and spread.

Intractable bleeding caused by radiation-induced gastritis is rare. We describe a 69-year-old man with intractable hemorrhagic gastritis induced by postoperative radiotherapy for the treatment of esophageal carcinoma. Although anti-secretory therapy with or without octreotide was initiated for hemostasis over three months, melena still occurred off and on, and the patient required blood transfusions to maintain stable hemoglobin. Finally growth hormone was used in the treatment of hemorrhage for two weeks, and hemostasis was successfully achieved. This is the first report that growth hormone has been used to control intractable bleeding caused by radiation-induced gastritis.

An STI-last integration scheme was successfully developed to fabricate low-defectivity and dopant-controlled SiGe SRB / sGe Fins. For the first time, 15 nm fin-width SiGe SRB/highly-strained Ge pFinFETs are demonstrated down to 35 nm gate length. With a CET INV -normalized G M,SAT,INT of 6.7 nm.mS/μm, the Si 0.3 Ge 0.7 / sGe pFinFETs presented in this work improve the performance by ~90% as compared to the state-of-the-art relaxed-Ge FinFETs.

This paper describes a novel scheme of metal gate integration to achieve precise threshold voltage (VTH) control and multiple VTH, by using metal composition and ion implantation (I/I) into work function metal (WFM). Moreover, WFM full fill is demonstrated with in situ barrier metal to satisfy the conductance requirement of sub-10 nm node gate.

In this article, we studied the photorefractive properties of Cu-doped (K0.5Na0.5)0.2(Sr0.75Ba0.25)0.9Nb2O6 (Cu:KNSBN) crystals with different doping levels. The properties include two-wave mixing and self-pumped phase conjugation, absorption properties, and the growth conditions as well. We also studied the effect of the dimensions on the photorefractive properties. The mechanism of Cu-doped KNSBN and the influence of the different sites occupied by Cu+ on photorefractive properties are also discussed. All the experimental results showed that doping levels have much effect on the photorefractive properties. The crystal with a higher doping level has a higher effective charge carrier density, a larger coupling coefficient, and a faster response rate, which is suitable for fast optical information processing. Dimension has much influence on the photorefractive properties. The thinner crystal with the same doping level has a larger coupling gain coefficient, and a shorter response time.

The reflectivity and time response of self-pumped phase conjugators using ii Cu-doped potassium sodium barium strontium niobiate (KNSBN:Cu) crystal in both internal and external geometries are investigated. The light source used is an Ar+ laser operating at 514.5 run, It was observed that the reflectivity remains constant at low power and begins to drop above a certain threshold power in both phase conjugators, and the response time of the internal phase conjugator increases with power, it was shown with two-beam coupling measurements that some of the observed phenomena result from a drop in the codirectional and contradirectional two-beam coupling gain coefficients of the crystal above a threshold intensity of 43 W cm-2. (C) 1998 Elsevier Science B.V.