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1.
Chem Asian J ; 2020 Feb 03.
Artigo em Inglês | MEDLINE | ID: mdl-32017408

RESUMO

Supramolecular co-assembling terpyridine-derivatives with nanoclay (LP) is exploited to acquire efficient amorphous room temperature phosphorescence (RTP). Experimental and theoretical investigations reveal that this coassembly not only brings about the configuration transforming from trans-trans (a) to cis-trans (a'') form via the protonating process, significantly narrowing the singlet-triplet energy gap, thereby effectively facilitate the single-triplet ISC processes, but well protects the triplet state and suppress the nonradiative transitions via restricting molecular rotation and vibration by the hydrogen bond interactions between them. Additionally, the flexible and transparent films through coassembling 1@LP (or 2@LP) with polyvinyl alcohol (PVA) also display excellent phosphorescence performance. Thanking to their distinctive RTP performances, the RH sensing and high-level data encryption are achieved.

2.
Medicine (Baltimore) ; 99(5): e18851, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-32000386

RESUMO

BACKGROUND: The pathogenesis of cervical spondylotic is degenerative changes of the cervical intervertebral disc, or bone hyperplasia of the posterior and hook joints, and instability of the joints of the cervical vertebrae. It causes the nerve roots to be stimulated and oppressed. The clinical manifestations are the sensation, movement, and reflex disorder of the cervical spinal nerve roots that are stimulated and oppressed, especially the numbness and pain of the neck, shoulders, upper limbs, and fingers. In this systematic review, we aimed to evaluate the efficacy and safety of acupuncture and chiropractic in the treatment of cervical spondylotic. METHODS AND ANALYSIS: We will search for PubMed, Cochrane Library, AMED, Embase, WorldSciNet; Nature, Science online and China Journal Full-text Database (CNKI), China Biomedical Literature CD-ROM Database (CBM), and related randomized controlled trials included in the China Resources Database. The time is limited from the construction of the library to September 2019. We will use the criteria provided by Cochrane 5.1.0 for quality assessment and risk assessment of the included studies, and use the RevMan 5.3 and Stata 13.0 software for meta-analysis of the effectiveness, recurrence rate, and symptom scores of cervical spondylotic. ETHICS AND DISSEMINATION: This systematic review will evaluate the efficacy and safety of acupuncture and chiropractic for cervical spondylotic. Because all of the data used in this systematic review and meta-analysis have been published, this review does not require ethical approval. Furthermore, all data will be analyzed anonymously during the review process trial.


Assuntos
Terapia por Acupuntura , Manipulação Quiroprática , Radiculopatia/terapia , Humanos , Radiculopatia/etiologia , Espondilose/complicações
3.
Org Lett ; 2020 Jan 28.
Artigo em Inglês | MEDLINE | ID: mdl-31990194

RESUMO

The spiroindoline skeleton featured with 2,7-diazaspiro[4.4]nonane exists in various structurally intricate and biologically active monoterpene indole alkaloids. A catalytic asymmetric cascade enamine isomerization/spirocyclization/dearomatization succession to construct the spiroindoline was developed, which employed the indolyl dihydropyridine as a substrate under catalysis of the chiral phosphoric acid. This cascade reaction provided various spiroindolines in both diastereoselective and enantionselective fashions.

4.
Psychiatr Serv ; : appips201800540, 2020 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-31960778

RESUMO

OBJECTIVE: Little is known about the role of primary care safety-net clinics, including federally qualified health centers and rural health clinics, in providing mental health services to youths. This study examined correlates and quality of mental health care for youths treated in these settings. METHODS: Medicaid claims data (2008-2010) from nine states were used to identify youths initiating medication for attention-deficit hyperactivity disorder (ADHD) (N=6,433) and youths with an incident depression diagnosis (N=13,209). The authors identified youths who received no ADHD or depression-related visits in a primary care safety-net clinic, some (but less than most) visits in these clinics, and most visits in these clinics. Using bivariate and regression analyses, they examined correlates of mental health treatment in these settings and whether mental health visits in these settings were associated with quality measures. RESULTS: Only 13.5% of the ADHD cohort and 7.2% of the depression cohort sought any ADHD- or depression-related visits in primary care safety-net clinics. Residence in a county with a higher (versus lower) percentage of residents living in an urban area was negatively associated with receiving the majority of mental health visits in these settings (p<0.05). Compared with youths with no visits in these settings, youths who received most of their mental health treatment in these settings received lower-quality care on five of six measures (p<0.01). CONCLUSIONS: As investment in the expansion of mental health services in primary care safety-net clinics grows, future research should assess whether these resources translate into improved mental health care access and quality for Medicaid-enrolled youths.

5.
J Phys Condens Matter ; 32(5): 055302, 2020 Jan 30.
Artigo em Inglês | MEDLINE | ID: mdl-31600739

RESUMO

Herein, thermoelectric properties of MoS2/MoSe2 lateral and van der Waals heterostructure are investigated by using density functional theory calculations and non-equilibrium Green's function method. Compared with pure MoS2, the thermoelectric performance of MoS2/MoSe2 lateral heterostructure is significantly improved due to the sharply decreased thermal conductance and slightly reduced power factor. Moreover, the thermoelectric performance can be further improved by constructing MoS2/MoSe2 van der Waals heterostructure. The room temperature ZT can reach 3.5, which is about 3 and 6 times greater than MoS2/MoSe2 lateral heterostructure and pure MoS2, respectively. This is because the strongly local electron and phonon states result in an ultralow thermal conductance in MoS2/MoSe2 van der Waals heterostructure. Furthermore, we also find that the thermoelectric performance of MoS2/MoSe2 van der Waals heterostructure is insensitive to contact areas due to the competing influence of PF and total thermal conductance. The current study presents an effective strategy to improve the thermoelectric performance of 2D heterostructures, which can be extended to a variety of materials for different applications.

6.
Polymers (Basel) ; 11(12)2019 Dec 02.
Artigo em Inglês | MEDLINE | ID: mdl-31810159

RESUMO

Isotactic polybutylene-1 (iPB) has lots of advantages and is best used as hot water pipe. However, to transform into stable crystal form I, the iPB needs as long as 7 days. In this process, the irreversible damage brings great difficulties to the use of the iPB. The method which convert it directly into crystal I has shortcomings such as being requiring complex operation and being expensive. In this study, an innovative idea was put forward, not paying attention to the crystal transformation of iPB but only focusing on reducing the time it can be applied. In this study, bamboo powder was modified by the silane coupling agent KH570 (KBP) to prepare iPB/KBP composite. The infiltration test and Fourier transform infrared (FTIR) analysis showed that the hydrophilicity of KBP is greatly reduced, which can greatly improve the compatibility of the iPB and KBP. The tensile strength, tensile modulus, flexural strength, and flexural modulus of the composites storage for 3 days is equal to the pure iPB with storage 7 days with the KBP additions of 3%, 3%, 7%, and 5%, respectively. The heat deformation temperature (HDT) of the composite with 3% KBP after 1-day storage reached the value of pure iPB storage for 7 days. This provides more space and possibilities for the industrialization of the iPB. The crystallization behavior of iPB/KBP composites proves that the addition of KBP accelerates the crystallization rate of iPB, but the crystallinity of the iPB/KBP composites is not changed. The SEM photograph of iPB/KBP composites showed that when the KBP addition was low the compatibility between KBP and iPB was good. When the KBP addition was increased the agglomeration of KBP in the iPB was very obvious, which leads to the poor mechanical properties of the composite.

7.
Med Phys ; 2019 Dec 24.
Artigo em Inglês | MEDLINE | ID: mdl-31872886

RESUMO

PURPOSE: In grating-based x-ray differential phase contrast (DPC) imaging, the measured signal amplitude of the phase shift induced by an image object is proportional to the so-called system sensitivity. Therefore, to achieve a better signal-to-noise (SNR) for improved imaging performance, it is generally believed that one should increase the system sensitivity by reducing the period of the analyzer grating or increasing the distance between the phase grating and analyzer grating. The purpose of this work is to theoretically and experimentally demonstrate that there is an optimal system sensitivity to attain the highest SNR for a given task provided that the standard phase-stepping acquisition and phase retrieval methods are used. When system sensitivity goes beyond this optimal value, SNR decreases and the imaging performance deteriorates. METHODS: Due to the fundamental fact that the measured phase signal is a cyclic variable, the phase wrapping effect is inevitable in DPC imaging when the system sensitivity increases. The phase wrapping effect appears in both signal and noise measurements. The effect in the signal measurement is manifested in the so-called signal statistical bias and such effect often impacts the accuracy of the measurement. The phase wrapping effect also appears in the noise variance measurement and impacts the precision of the measurement. A thorough theoretical analysis was performed in this work to demonstrate the quantitative impacts of phase wrapping on both signal bias and noise variance and thus on the actual system SNR. The joint effect of phase wrapping in both the signal bias and noise variance yields an optimal system sensitivity to achieve the highest SNR. Both extensive numerical simulation studies and experimental studies were performed to validate the theoretical analysis. RESULTS: Both theoretical analysis and experimental studies show that the SNR of the DPC signal is not always proportional to the sensitivity due to the cyclic nature of the signal and the phase wrapping effect. For a given refraction angle and exposure level, there exists an optimal sensitivity factor that maximizes the SNR, beyond which, increasing the sensitivity will decrease the SNR. CONCLUSIONS: Increase of system sensitivity does not always improve x-ray DPC imaging performance provided that the standard phase-stepping acquisition and phase retrieval methods are used.

8.
Toxins (Basel) ; 12(1)2019 Dec 19.
Artigo em Inglês | MEDLINE | ID: mdl-31861743

RESUMO

To explore the protective role of hydrogen gas (H2) on oxidative damage and apoptosis in intestinal porcine epithelial cells (IPEC-J2) induced by deoxynivalenol (DON), cells were assigned to four treatment groups, including control, 5 µM DON, H2-saturated medium, and 5 µM DON + H2-saturated medium treatments. After 12 h of different treatments, the cell viability, biomarkers of cell redox states, and gene expression of antioxidant enzymes and apoptosis were observed and detected. Furthermore, caspase-3 and Bax protein expressions were measured by Western blot analysis. Our results demonstrated that the 5 µM DON significantly caused cytotoxicity to IPEC-J2 cells by reducing cell viability and increasing lactate dehydrogenase release in culture supernatants. Moreover, DON treatments significantly increased levels of 8-hydroxy-2'-deoxyguanosine, 3-nitrotyrosine, and malonaldehyde; however, they decreased total superoxide dismutase and catalase activities and downregulated messenger RNA (mRNA) expression related to antioxidant enzymes in cells. The 5 µM DON treatment also downregulated Bcl-2 expression and upregulated caspase-3 and Bax expression. However, the H2-saturated medium significantly improved cell growth status and reversed the change of redox states and expression of genes and proteins related to apoptosis induced by DON in IPEC-J2 cells. In conclusion, H2 could protect IPEC-J2 cells from DON-induced oxidative damage and apoptosis in vitro.

9.
J Sci Food Agric ; 2019 Nov 22.
Artigo em Inglês | MEDLINE | ID: mdl-31756265

RESUMO

BACKGROUND: Baixi sufu (BS) is a traditional Chinese spicy fermented bean curd manufactured with a natural starter. In this study, the bacterial and fungal communities during BS fermentation were determined by culture and by the culture-independent method of high-throughput sequencing (HTS). Correlation analyses were performed to select the microorganisms potentially contributing to this fermentation. RESULTS: During the fermentation of BS, 162 bacterial and 97 fungal strains were isolated and identified, and a total of 268 314 bacterial and 287 844 fungal high-quality sequences were analyzed. In general, lactic acid bacteria (LAB), especially Enterococcus and Lactococcus, were dominant in the early stage of fermentation, and spore-forming bacteria, especially Bacillus spp., became the predominant bacteria by the end of fermentation. Geotrichum, Mortierella, and unclassified Ascomycota, were the major fungal populations, which could not be detected in the final product. Correlation analyses indicated that Enterococcus, Bacillus, Geotrichum, and unclassified Ascomycota correlated significantly and positively with amino nitrogen. However, due to the sporulation characteristics of Bacillus, they may have little effect on BS ripening. The presence of Bifidobacterium spp. in sufu is reported for the first time, but the excessive counts of the Bacillus cereus group (>105 CFU g-1 ) indicate a potential hazard to consumers. CONCLUSION: The profiles obtained from this study will contribute to the development of autochthonous starter cultures to control BS fermentation, and may lead to the development of novel strategies to shorten the fermentation time of sufu products. © 2019 Society of Chemical Industry.

10.
Int J Infect Dis ; 89: 66-71, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31521852

RESUMO

OBJECTIVES: To determine blood Brucella DNA loads between brucellosis patients and those without brucellosis. METHODS: The patient group included 350 brucellosis patients. The control was composed of 200 subjects without brucellosis. The extracted DNA from blood was tested by quantitative polymerase chain reaction (qPCR). The cutoff value was determined by receiver operating characteristic curve analysis. A portion of the brucellosis patients were monitored by qPCR during therapy. RESULTS: The detection limit of qPCR was between 1E+01cfu/µL and 1E+08cfu/µL. The standard curve R2 reached 0.998. The cutoff value was 4E+01cfu/µL, which was determined by comparison of the patient group and the control. The qPCR assay had a specificity of 100% and a sensitivity of 93.14%. The monitoring results showed that the Brucella DNA load decreased in most patients during the first 4 weeks of treatment. One patient with bad treatment compliance showed a rebound. CONCLUSIONS: The qPCR results were in accordance with the course of brucellosis in the clinic. The DNA load often reflects the situation of the Brucella-infected patient. The cutoff value provides an important reference of infection. This qPCR-based method can be used to assist in the diagnosis of brucellosis and to adjust the therapy.

11.
Phys Med Biol ; 64(21): 215014, 2019 Oct 31.
Artigo em Inglês | MEDLINE | ID: mdl-31509812

RESUMO

Non-contrast CT (NCCT) is widely employed as the first-line imaging test to evaluate intracranial hemorrhage (ICH). Advances in mutidetector CT (MDCT) technology have greatly improved the image quality of NCCT for the detection of established, relatively large, and acute ICHs. Meanwhile, the reliability of MDCT in detecting microbleeds and chronic hemorrhage, and in predicting hemorrhagic transformation needs to be further improved. The purpose of this work was to investigate the potential use of non-spectral photon counting CT (PCCT) to address these challenges in ICH imaging. Towards this goal, the NCCT protocol of an experimental PCCT system that simulates the geometry of a general-purpose MDCT was optimized. The optimization was driven by three imaging tasks: detection of a 4.0 mm intraparenchymal hemorrhage, detection of a 1.5 mm subarachnoid hemorrhage, and discrimination of a sulcus in the insular cortex from the parenchymal background. These imaging tasks were custom-built into an anthropomorphic head phantom. Under the guidance of the frequency-dependent noise equivalent quanta and the ideal observer model detectability index [Formula: see text], the optimal PCD detection mode, energy threshold, and reconstruction kernel were found to be the anti-charge sharing mode, 15 keV, and an apodized ramp kernel, respectively. Compared with a clinical MDCT operated with an ICH protocol and at a matched dose level, the PCCT system provided at least 20% improvements in [Formula: see text] for all three ICH imaging tasks. These results demonstrated the potential benefits of non-spectral PCCT in ICH assessment.

12.
J Phys Condens Matter ; 31(50): 505303, 2019 Sep 05.
Artigo em Inglês | MEDLINE | ID: mdl-31487697

RESUMO

Phonon transport in periodically modulated cylindrical nanowire (PMCN) and quasi-periodically modulated cylindrical nanowire (QPMCN) is comparatively studied. It is shown that the transmission coefficient and thermal conductance for PMCN is greater than the corresponding values for QPMCN. At low frequencies, a wide stop-frequency gap due to the destructive interference between the incoming and back waves can be clearly observed here. For PMCN, such stop-frequency gap seems to be insensitive to the change of N (the periodic number). For QPMCN, however, its breadth increases with the increase of N (the Fibonacci number). When N is increased, the thermal conductance for PMCN presents a distinct change from the decrease to the constant, while QPMCN has a tendency of monotonous decrease. A brief discussion on these results is made.

13.
ACS Nano ; 13(8): 9091-9099, 2019 Aug 27.
Artigo em Inglês | MEDLINE | ID: mdl-31393706

RESUMO

While pseudocapacitive electrodes have potential to store more energy than electrical double-layer capacitive electrodes, their rate capability is often limited by the sluggish kinetics of the Faradaic reactions or poor electronic and ionic conductivity. Unlike most transition-metal oxides, MoO2 is a very promising material for fast energy storage, attributed to its unusually high electronic and ionic conductivity; the one-dimensional tunnel is ideally suited for fast ionic transport. Here we report our findings in preparation and characterization of ultrathin MoO2 sheets with oriented tunnels as a pseudocapacitive electrode for fast charge storage/release. A composite electrode consisting of MoO2 and 5 wt % GO demonstrates a capacity of 1097 C g-1 at 2 mV s-1 and 390 C g-1 at 1000 mV s-1 while maintaining ∼80% of the initial capacity after 10,000 cycles at 50 mV s-1, due to minimal change in structural features of the MoO2 during charge/discharge, except a small volume change (∼14%), as revealed from operando Raman spectroscopy, X-ray analyses, and density functional theory calculations. Further, the volume change during cycling is highly reversible, implying high structural stability and long cycling life.

14.
Med Care ; 57(8): 574-583, 2019 08.
Artigo em Inglês | MEDLINE | ID: mdl-31295187

RESUMO

BACKGROUND: Medicaid is an important source of insurance coverage for those with mental health (MH) disorders in the United States. Although disruptions in Medicaid coverage are common, little is known about the dynamic relationship between Medicaid disenrollment and MH care utilization. OBJECTIVE: We estimated changes in all-cause and MH-related health care use post Medicaid disenrollment among a nationwide cohort of adults with MH disorders. SUBJECTS: We identified 8841 persons (197,630 person-months) ages 18-64 with MH disorders and Medicaid coverage from Panels 4 to 19 Medical Expenditure Panel Survey. METHODS: Using a quasi-experimental design and propensity weighting, we estimated logit models examining changes in service utilization per-person-per-month. We used a "post" indicator to estimate average differences in service use postdisenrollment (vs. those with continuous Medicaid coverage) and a count variable measuring total months since coverage loss to estimate changes over time. OUTCOME MEASURES: All-cause outpatient visits, MH-related outpatient visits, and acute care visits. RESULTS: Becoming uninsured after Medicaid disenrollment was associated with average reductions of 52% [-14.75 percentage-points, 95% confidence interval (CI): -17.59, -11.91] in the likelihood of receiving any outpatient service, 35% (-2.23 percentage-points, 95% CI: -3.71, -0.75) in the likelihood of receiving any MH-related outpatient service, and 52% (-2.44 percentage-points; 95% CI: -3.35, -1.52) in the likelihood of receiving any acute service in a month. Health care use declined the most in the month immediately postdisenrollment, and declines continued over the next half-year (while uninsured). CONCLUSIONS: Insurance loss after disenrollment from Medicaid led to a persistent disruption in the receipt of health care services for beneficiaries with MH disorders.


Assuntos
Medicaid/estatística & dados numéricos , Transtornos Mentais/terapia , Aceitação pelo Paciente de Cuidados de Saúde/estatística & dados numéricos , Adolescente , Adulto , Feminino , Custos de Cuidados de Saúde/estatística & dados numéricos , Nível de Saúde , Humanos , Masculino , Pessoas sem Cobertura de Seguro de Saúde/estatística & dados numéricos , Pessoa de Meia-Idade , Fatores Socioeconômicos , Estados Unidos , Adulto Jovem
15.
Am J Transl Res ; 11(6): 3412-3425, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31312354

RESUMO

BACKGROUND: Glucose metabolism is an essential energy source for mammalian preimplantation embryonic development. Therefore, we aimed to analyze the expression of all 12 known glucose transporters (facilitated solute carrier family 2, Slc2a) during early mouse embryo development. METHODS: Gene and protein expression of Slc2a transporters in oocytes and embryos were assessed by the TaqMan gene expression assay and confocal immunofluorescence, respectively. RESULTS: Except for Slc2a2, the other 11 Slc2a transcripts were detected in oocytes. Transcripts of Slc2a1, Slc2a3, Slc2a4, and Slc2a8 were the most enriched and detected in preimplantation embryos. The transcription of other Slc2a isoforms was barely detectable or absent after fertilization; however, they were detected in blastocysts, except for Slc2a10 and Slc2a13. Embryo culture in the simple defined medium caused a reduction in transcription of Slc2a1, Slc2a3, Slc2a4, and Slc2a8 in blastocyst; yet, amino acids partially reversed this impaired transcription of Slc2a1 and Slc2a4. SLC2A1 and SLC2A4 proteins were detected at all embryonic stages with nuclear accumulation in the embryos at the early cleavage stage. SLC2A3 and SLC2A8 were not detected in embryos until the eight-cell stage. The cellular membrane localization of SLC2A1, SLC2A3, and SLC2A8 occurred after compaction and was characterized in blastocysts. SLC2A4 was evenly distributed in the cytoplasm and nuclei without its characteristic membrane localization. Indinavir sulfate (a SLC2A4 inhibitor) decreased the rate of development and prevented glucose utilization in embryos after compaction. These inhibitory activities were partially reversed by exogenous insulin. CONCLUSION: The results unveil distinct expression patterns of individual Slc2a glucose transporters during early embryo development. Taken together, they provide novel insights into the understanding and management of glucose metabolic infertility in assisted-reproductive technologies (ART).

16.
Phys Med Biol ; 64(18): 185015, 2019 09 19.
Artigo em Inglês | MEDLINE | ID: mdl-31315093

RESUMO

While CTA is an established clinical gold standard for imaging large cerebral arteries and veins, an important challenge that currently remains for CTA is its limited performance in imaging small perforating arteries with diameters below 0.5 mm. The purpose of this work was to theoretically and experimentally study the potential benefits of using photon counting detector (PCD)-based CT (PCCT) to improve the performance of CTA in imaging these small arteries. In particular, the study focused on an important component of the CTA image package known as the maximum intensity projection (MIP) image. To help understand how the physical properties of a detector quantitatively influence the MIP image quality, a theoretical model on the statistical properties of MIP images was developed. After validating this model, it was used to explore the individual and joint contribution of the following detector properties to the MIP signal-to-noise ratio (SNR): inter-slice noise covariance, spatial resolution along the z direction, and native pixel pitch along z. The model demonstrated that superior slice sensitivity, reduced inter-slice noise correlation, and smaller native pixel pitch along z provided by PCDs lead to improved vessel SNR in MIP images. Finally, experiments were performed by scanning an anthropomorphic cerebral angiographic phantom using a benchtop PCCT system and a commercial MDCT system. The experimental MIP results consistently demonstrated that compared with MDCT, PCCT provides superior vessel conspicuity and reduced artifactual stenosis.

17.
Phytochemistry ; 166: 112065, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31362147

RESUMO

Ten undescribed neo-clerodane diterpenoids, named hispanins A-J, together with six known ones, were isolated from the aerial parts of Salvia hispanica L. Their structures were established by extensive spectroscopic analysis. The absolute configurations of the undescribed compounds were determined by the ECD data and single crystal X-ray diffraction analysis. Hispanins B and C represented the first neo-clerodane diterpenoids with a unique oxygen bridge between C-19 and C-20. All isolated compounds were evaluated for their protective effects against H2O2-induced cardiomyocyte injury. Five of these compounds showed significant cardioprotective effects.


Assuntos
Cardiotônicos/química , Cardiotônicos/farmacologia , Diterpenos Clerodânicos/química , Diterpenos Clerodânicos/farmacologia , Componentes Aéreos da Planta/química , Salvia/química , Animais , Miócitos Cardíacos/citologia , Miócitos Cardíacos/efeitos dos fármacos , Miócitos Cardíacos/metabolismo , Ratos
18.
Artigo em Inglês | MEDLINE | ID: mdl-31068738

RESUMO

The sensitivity factor of a grating-based x-ray differential phase contrast (DPC) imaging system determines how much fringe shift can be observed for a given refraction angle. It is commonly believed that increasing the sensitivity factor will improve the signal-to-noise ratio (SNR) of the phase signal. However, this may not always be the case if the intrinsic phase wrapping effect is taken into consideration. In this work, a theoretical derivation is provided to quantify relationship between the sensitivity and SNR for a given refraction angle, exposure level, and grating based x-ray DPC system. The theoretical derivation shows that the expected phase signal is not always proportional to the sensitivity factor and may even decrease when the sensitivity factor becomes too large. The noise variance of the signal is not always solely dependent on the exposure level and fringe visibility but may become signal-dependent under certain circumstances. As a result, SNR of the phase signal does not always increase with higher sensitivity. Numerical simulation studies were performed to validate the theoretical models. Results show that when the fringe visibility and exposure level are fixed, there exists an optimal sensitivity factor which maximizes the SNR for a given refraction angle; further increase of the sensitivity factor may decrease the SNR.

19.
Artigo em Inglês | MEDLINE | ID: mdl-31105375

RESUMO

In 1963, Shaw applied Fourier analysis to the zero-frequency DQE and developed the frequency-dependent DQE or DQE(k) and made it clear that DQE(k) is applicable to every frequency level within the system bandwidth, including the zero frequency. Over time, especially after entering the modern era of digital x-ray imaging, the experimental measurement methods of DQE(k) (particularly the measurements of the NPS which is an important element in DQE(k)) have evolved, and some measurement methods may generate nonphysical NPS and DQE results at k=0. As a result, an experimental DQE(k) curve is often cut off at certain low frequency above zero. This work presents a new experimental method to deal with two challenges: severe NPS(k=0) underestimation due to polynomial-based background detrending; severe NPS(k=0) overestimation due to the presence of faint but non-negligible system drift. Based on a theoretical analysis of the impact of drift to the measured autocovariance function, the error introduced by drift can be isolated, and corresponding correction can be applied to NPS(k=0). Both numerical simulation with known ground truth and experimental studies demonstrated that the proposed method enables accurate DQE(k=0) measurement.

20.
Polymers (Basel) ; 11(3)2019 Mar 18.
Artigo em Inglês | MEDLINE | ID: mdl-30960492

RESUMO

Isotactic polypropylene (iPP) is a commonly used thermoplastic polymer with many excellent properties. But high brittleness, especially at low temperatures, limits the use of iPP. The presence of transcrystallization of iPP makes it possible for fiber-reinforced iPP composites with higher strength. Bacterial cellulose (BC) is a kind of cellulose with great potential to be used as a new filler to reinforce iPP due to its high crystallinity, biodegradability and efficient mechanical properties. In this study, the iPP/BC hamburger composite was prepared by a simple hot press and maleic anhydride grafted polypropylene (MAPP) was used to improve the interface compatibility of iPP and BC. The polarizing microscope (POM) photograph shows that BC successfully induces the transcrystallization of iPP. The differential Scanning Calorimeter (DSC) date proves that the addition of BC could improve the thermal properties and crystallization rate of the composite. Especially, this change is more obvious of the iPP/MAPP/BC. The mechanical properties of the iPP/BC composites were greatly increased. This DSC date is higher than BC; we used BC particles to enhance the iPP in our previous research. The scanning Electron Microscope (SEM) analysis intuitively shows that the interface of the iPP/MAPP/BC is more smooth and flat than the iPP/BC. The fourier Transform infrared spectroscopy (FT-IR) analysis of the iPP/BC hamburger composites was shown that a new C=O group vibration appeared at 1743 cm-1, which indicated that the hydrogen bond structure of BC molecules was weakened and some hydroxyl groups were substituted after modification which can increase the lipophilicity of BC. These results indicated that the BC fiber can easily induce the transcrystallization of iPP, which has excellent mechanical properties. Moreover, the addition of MAPP contributes greatly to the interface compatibility of iPP and BC.

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