High ΔK Research Articles

Pre- to post-dialysis potassium gradient and mortality in patients on hemodialysis: A propensity-matched analysis.

Pre- to post-dialysis potassium gradient (ΔK) has arrhythmogenic effects; however, its effect on mortality remains unclear. The relationship between ΔK and mortality was assessed. All patients undergoing hemodialysis in Beijing in 2014 were eligible for inclusion. The low (≤1.2 mmol/L), median (1.2-1.8 mmol/L), and high (>1.8 mmol/L) ΔK groups were matched by sex, age, diabetes, and dialysis time for enrollmen. The primary and secondary outcomes were all-cause and cardiovascular death within the follow-up. Cox regression analysis was performed to evaluate the effect of ΔK on mortality. We also analyzed the associations of combinations of ΔK and pre-dialysis potassium with mortality. We enrolled 2181 patients in three matched groups (n = 727 per group). The median follow-up was 72.0 (interquartile range, 53.7-72.0) months. All-cause mortality occurred in 215/727 (29.6%), 95/727 (13.1%), and 198/727 (27.2%) patients in the low-, median-, and high-ΔK groups, respectively. After adjusting for multiple factors, the median ΔK group had better survival than the low- (hazard ratio (HR), 1.91; 95% confidence interval [95% CI], 1.45-2.52; p < 0.001) and high-ΔK groups (HR, 2.17; 95% CI, 1.57-2.99; p < 0.001). Further analysis based on pre-dialysis potassium revealed that when maintaining a level of 4.5-5.5 mmol/L and ΔK of 1.2-1.8 mmol/L, patients had the lowest risk of mortality, whereas the highest risk was observed when pre-dialysis potassium was >5.5 mmol/L and ΔK was >1.8 mmol/L. Maintaining serum potassium within a appropriate range and reducing potassium fluctuations during dialysis may help to reduce the mortality risk of maintenance hemodialysispatients. These findings provide important data support for the quality control of hemodialysis.

Influence of load ratio on fatigue life assessment of AZ31B magnesium alloy under different temperatures

First ever fatigue crack growth experiments were conducted under various load ratios (R = 0.1 to 0.8) at 300 K, and (R = 0.1, 0.3, 0.5, and 0.7) at 327 K and 473 K, respectively, on AZ31B magnesium alloy. The results reveal that temperature-dependent variations in both fatigue crack growth rates and stress intensity factor ranges (ΔK) across different load ratios. It was found that at relatively higher load ratio (R = 0.8) leads to a lower ΔK = 8.0287 MPa√m and a lower load ratio (R = 0.1) result in a higher ΔK = 15.5981 MPa√m, indicating that the material undergoes fatigue crack propagation at a higher level of stress intensity factor range at room temperature. A slower crack propagation was seen at higher load ratio (R = 0.8), whereas lower load ratio (R = 0.1) exhibits faster crack growth at 300 K. Similarly, crack growth generally increases at higher temperatures (i.e., 373 K and 473 K). The fatigue life of the magnesium alloy AZ31B increased from 12,410 to 87,031 cycles at 300 K, 9,620 to 32,667 cycles at 373 K, and 9,140 to 30,143 cycles at 473 K as the load ratio increases. The average fatigue life decreases to 59 % and 63 % as the temperature is varied from 300 K through 373 K to 473 K. The fractographic and surface roughness carried out by field emission scanning electron microscopy and 3D-Profilometer respectively, illustrate that roughness of fracture surfaces correlates with an increase in the fatigue crack growth rate for a specific value of ΔK.

Abstract 3008: Aortic Arch Endovascular Stent Grafts With Zone 0 Proximal Landing Zones For Geometrically Complex Aortas

Objectives: Fluctuation in total curvature (δK) significantly outperforms all other available measurements of shape in predicting clinical outcomes after thoracic endovascular aortic repair (TEVAR). We aim to identify if the Nexus® Aortic Arch Stent Graft System is a suitable and safe treatment modality for aortas with high δK. Methods: Twenty-five patients that underwent transcatheter aortic arch repair using the Nexus stent graft were included. 3D aortic models were segmented from the CTA image data using Simpleware ScanIP. The aorta segmentations were then smoothed and the outer surface isolated. A triangular mesh from the outer surface was generated in Python, and the mesh was divided into a number of partitions. δK was calculated by the sum of per partition total curvatures and the fluctuation in total curvature across the entire manifold surface. Failed TEVAR was defined by a) any device-related mortality or b) unplanned or device-related secondary surgical intervention 30 days from index TEVAR. This data was plotted into a pre-defined (δK,L –1 )-feature space with pre-established machine learning-derived boundary conditions. Results: Within a (δK,L –1 )-feature space defined by patients with aortic stent grafts with zone 2 or 3 proximal landing zones, our group used predictive modeling to classify patients into three zones (normal, successful TEVAR, and unsuccessful TEVAR) with 92.8% mean accuracy. Within this pre-defined boundary zone of unsuccessful TEVAR, 72.2% (13/18) of patients with the Nexus stent graft with zone 0 proximal landing zone underwent a successful TEVAR without need for re-intervention. Conclusions: Transcatheter aortic arch repair with a single branch, two-stent graft system with a zone 0 proximal landing zone can offer patients with a high degree of aortic shape fluctuation a greater chance at successful TEVAR than traditional aortic stent grafts with zone 2 or 3 landing zones.

Comparison of fatigue crack growth behaviour in electron-beam and laser powder-bed-fusion Inconel 718

A comparative study on fatigue crack growth behaviour was made between the electron-beam powder-bed-fusion (PBF-EB) and laser powder-bed-fusion (PBF-LB) Inconel 718. The crack followed a transgranular path with a faster propagation rate for the PBF-EB Inconel 718, whereas a combination of intergranular and transgranular path was observed for the PBF-LB, and its slower rate being comparable to the wrought counterpart. The main fatigue crack in the PBF-EB Inconel 718 exhibited a sawtooth shaped path at the micro-scale, with intensive slip traces close to the crack surfaces owing to the very low work hardening rate. Based on the digital image correlation (DIC) analysis of the crack tip field, fatigue-crack sawtooth path in the PBF-EB Inconel 718 can be successfully predicted by using a strain energy density criterion, which dictates the crack growth follows the direction of minimum distance from the crack tip to elasto-plastic boundary. For the PBF-LB Inconel 718, the predominant fatigue crack was straight at low ΔK, but severe deflections occurred at the medium and high ΔK regimes. A clear correlation exists between the incipient intergranular cracks and the main crack path deflection. This suggests that once the accumulated damage in the plastic zone around the crack tip reaches the critical value, intergranular cracks can form the new front of the fatigue crack, causing the main crack path deflection. Elasto-plastic fracture mechanics parameters of rp and ΔCTOD, derived from the DIC-based crack tip field analysis, can qualitatively predict the lower crack growth rate of the PBF-LB Inconel 718.

On the low temperature fatigue crack growth behavior of AA7075-T651 in ultra-high vacuum environments

It is well-established that the fatigue crack growth behavior of aerospace aluminum alloys in high altitude applications is sensitive to both temperature and water vapor pressure. To isolate the role of temperature, fatigue crack growth experiments were performed on AA7075-T651 under ultra-high vacuum conditions (<6x10−6 Pa) at temperatures ranging from 23 °C to −65 °C. All da/dN–ΔK relationships exhibit the following: (1) a temperature-independent Paris regime at high ΔK, (2) a transition from the Paris regime to a sharply reduced da/dN, which occurs at higher ΔK as the temperature decreases, and (3) a coalescence in da/dN for all temperatures in the threshold region. Interestingly, the point of deviation from the Paris regime is found to correlate with a transition from a flat, transgranular fracture morphology to slip band cracking (SBC) across all conditions. The likely mechanisms governing the observed behaviors are discussed, focusing on the role of slip.

Fatigue crack initiation and competitive crack propagation behavior in 500 MPa grade automobile beam steel

The fatigue crack initiation and propagation in Nb–Ti micro-alloyed 500 MPa grade steels that usually be used in the automobile beam were investigated. Reducing the content of C and Mn elements based on the reference steel and adding microalloying elements Nb and Ti to obtain the modified steel. The fatigue strengths of the reference steel and the modified steel are 201 MPa and 225 MPa, respectively. Fatigue cracks in the experimental steel were initiated at surface defects and persistent slip bands (PSBs). The modified steel is more susceptible to initiating cracks at the PSBs than the reference steel. There were three kinds of fracture modes in the experimental steels, which were determined by the competition between carbide and inclusion. As the loading stress and the stress intensity factor (Δk) increase, the fracture mode transforms from cleavage (brittle) to dimple (ductile) fracture. Under the circumstance of low loading stress and low Δk, the fracture mode is dominated by the carbide-induced cleavage fracture mechanism. Under the situation of high loading stress and Δk, the fracture mode is dominated by the inclusion-induced dimple fracture mechanism. In addition, the mixed cleavage-dimple region is formed when the two fracture mechanisms compete in the steel.

Corrosion fatigue crack growth behavior of a structurally gradient steel for high-speed railway axles

Considering the complex service environments that high speed railway axles are subjected to, the fatigue crack growth (FCG) behavior of a structurally gradient axle steel with different pre-crack depths both in air and a corrosive medium was investigated at a frequency of 5 Hz. The results indicated that in the high ΔK region, the FCG rate was dramatically accelerated by corrosion but the gap narrows as ΔK decreased. The accelerated corrosion FCG rate was a comprehensive result of the acceleration effect of the anodic dissolution, hydrogen-enhanced localized plasticity and the retardation effect of corrosion-induced crack-tip blunting. Despite the fact that the corrosion resistance gradually decreased as the pre-crack depth increased, the FCG rate in the corrosive medium gradually decreased. This was because fatigue loading played a more important role than corrosion in accelerating the corrosion FCG rate.

Temperature and ΔK dependence of grain boundary effect on fatigue crack propagation in a two-dimensional polycrystalline Ni-base superalloy

Effects of grain boundaries (GBs) on fatigue crack propagation (FCP) in a cast Ni-base superalloy were experimentally investigated using “two-dimensional” polycrystalline specimens extracted from a directionally solidified material. FCP tests were conducted at room temperature (RT), 700 °C and 900 °C under the stress intensity factor range, ΔK, increasing conditions, and distinctive FCP behavior both in grain interiors and around the GBs was observed in-situ. At RT, the crack propagated in the shearing mode along slip planes. At 700 °C, the cracking mode transitioned from the opening mode to the shearing mode with the increasing ΔK. At 900 °C, only the opening mode cracking occurred. The shearing cracks at RT and in the high ΔK region at 700 °C were retarded near the GBs, whereas the opening mode crack in the low ΔK region at 700 °C was not affected by the GBs. The retardation was attributed to a transition from the shearing mode to the opening mode induced by the slip plane incompatibility at the GBs, and the degree of the retardation showed a good correlation with the size of the shearing crack plane. At 900 °C, the crack propagated along high angle GBs with higher FCP rates than those in grain interiors. The acceleration was greater at the GBs with larger misorientation, which was attributed to higher GB energy. In high ΔK regions, secondary cracks were nucleated along high angle GBs ahead of main crack tips possibly because of external stress normal to the GBs and/or the strain incompatibility at the GBs.

Effect of Microstructure on the Corrosion Fatigue Crack Growth of Low and Medium Steels

This article studies the effect of microstructure on the corrosion fatigue crack growth behavior of low and medium carbon steels. 45 steel and 15CrMo were selected and five typical microstructures were obtained by different heat treatment processes. The microstructures of 45 steel and 15CrMo after annealing and normalizing are both ferrite and pearlite, but the proportions of ferrite and pearlite in the four microstructures are different. The quenching and tempering microstructure of 45 steel is tempered fine pearlite. Corrosion fatigue tests were conducted on specimens with different microstructures of the two materials. Expressions of corrosion fatigue crack growth rate and da/dN∼ΔK fitting curves of different microstructures were obtained. Comparison of da/dN∼ΔK curves of 45 steel shows that tempered fine pearlite has the best resistance to corrosion fatigue crack growth, and the content of pearlite has a great impact on the corrosion fatigue crack growth behavior for specimens with the microstructure of ferrite and pearlite. In the low ΔK region, the corrosion factor plays a dominant role in fatigue crack growth, and the corrosion resistance of pearlite is weak, which leads to a higher da/dN in the normalized state. In the high ΔK region, fatigue factor dominants, since the fatigue resistance of pearlite is strong, da/dN of the annealed state is higher. The experimental results of 15CrMo showed the same crack growth rate change regulation as that of 45 steel, which further proves the effect of pearlite on the corrosion fatigue crack propagation behavior.

Revealing the fatigue crack propagation mechanism of a Ni-based superalloy electron beam welded joint through in-situ SEM observation

In this study, in-situ scanning electron microscope (SEM) fatigue crack propagation experiments for electron beam welded joints of GH4169 Ni-based superalloy are carried out. Based on material characterization and analysis, the corresponding fatigue crack propagation mechanism of the welded joint (WJ) is investigated. Compared to the base material (BM), the WJ has comparable static strength, but worse plasticity. Significantly, the WJ has longer fatigue crack growth life than that of the BM. The fatigue crack growth rate (FCGR) curves of the WJ and the BM intersected with each other. In particular, under low stress intensity factors (ΔK) level, the FCGR of the WJ is lower than that of the BM. Under high ΔK level, the FCGR of the WJ is higher than that of the BM. The steep FCGR curve of the WJ can be attributed to the unique weld texture and a shielding effect caused by the weld strength mismatch.

A new fatigue crack growth mechanism of high-strength steels

In this study, the fatigue crack damage evolution procedure of AISI 4340 high-strength steel was systematically studied via three-dimensional X-ray technology and scanning electron microscopy. Based on the experimental results and theoretical analysis, a new FCG mechanism is proposed, i.e. the blunting and re-sharpening to micro-scale void coalescence (BRS-MVC) mixed mechanism. Few micro-scale voids initiated near the crack tip are surrounded by the blunting crack tip at low ΔK zone, which is controlled by the BRS mechanism. More micro-scale void clusters would occur around the crack tip at high ΔK zone, which may be attributed to the MVC mechanism. The new FCG mechanism provides a unique perspective for the FCG behavior of high-strength steels, which could promote the fatigue life prediction of metallic materials.

Hydrogen‐assisted fatigue crack propagation behavior of equiatomic Co–Cr–Fe–Mn–Ni high‐entropy alloy

AbstractThe equiatomic Co–Cr–Fe–Mn–Ni high‐entropy alloy (HEA) shows well hydrogen embrittlement resistance under monotonic tensile load. However, the fracture behavior under cyclic load is still unclear. In this study, combining with the fracture features analysis by electron back‐scattered diffraction and electron channeling contrast imaging techniques, the hydrogen‐assisted fatigue crack propagation behavior of equiatomic Co–Cr–Fe–Mn–Ni HEA under in situ electrochemical hydrogen charging was investigated. The results suggest that the hydrogen had significant accelerating effects on the fatigue crack growth rate of Co–Cr–Fe–Mn–Ni HEA. Intergranular cracking with the formation of dislocation cells was observed at low stress intensity range (ΔK) area, while transgranular cracking with deformation twins was observed at a high ΔK area. The formation of these deformation features was assisted by hydrogen‐assisted dislocation emission.

Corneal epithelial thickness analysis of forme fruste keratoconus with optical coherence tomography.

To explore the significance of corneal epithelial thickness analysis in diagnosing early keratoconus. There were 26 clinical keratoconus, 21 forme fruste keratoconus, 40 high corneal astigmatism (ΔK) and 40 low ΔK eyes involved in the study. Fourier-domain optical coherence tomography was used to measure the corneal epithelial thickness of four groups. The morphological features of topographic map and the thickness of corneal epithelial thinnest point were analyzed. The distribution curve of corneal epithelial thickness at 45°, 90°, and 135° axial directions that are through the pupil center was also analyzed. One-way ANOVA was performed to compare the data. The topographic map of forme fruste keratoconus corneal epithelial thickness was uniformity shape; crater shape existed only in clinical keratoconus group; and central island shape mainly existed in high ΔK group. The thinnest point of corneal epithelial thickness of forme fruste keratoconus group was significantly lower than that of low ΔK group (P=0.022). The thickness of corneal epithelium in the forme fruste keratoconus at 90° was thinner than that in the low astigmatism group at -1, and -2 mm points (P -1 mm=0.015, P -2 mm=0.036). The analysis of the thinnest point in forme fruste keratoconus corneal epithelium appears earlier than corneal epithelial remodeling. The topographic map of corneal epithelium in high ΔK eyes appears in central island shape, and can be used for the differential diagnosis of early keratoconus.

Development of a Diversity Panel for Traditional Rice (Oryza Sativa L.)Accessions/Varieties in Sri Lanka

Oryza sativa L. varieties grown in Sri Lanka from ancient times to the middle of the last century are known as traditional rice varieties and a collection of over 2000 traditional rice accessions conserved at Gene Bank, Plant Genetics Resource Center (PGRC), Peradeniya, Sri Lanka. Farmers preferred traditional rice varieties for their adaptability to biotic and abiotic stresses and are an important component of the biodiversity of Sri Lanka. A detailed understanding of the genetic structure and diversity of traditional rice varieties is essential for the effective utilization of rice genetic resources and identification of potential parents possessing valuable genetic traits for future crop improvement in rice breeding programmes. The objective of the present study was phenotypic and molecular characterization of one hundred (100) traditional rice accession/varieties collected from PGRC, Sri Lanka and identification of a broad diversity panel for these traditional rice accessions/varieties. Rice varieties were grown in a plant house following Randomized Complete Block design with 4 replicates and 5 plants per each replicate. Thirty-two (32) agro-morphological characters were observed. Green leaves of rice varieties were individually collected from 20 day-old seedlings for gDNA extraction using Plant genomic DNA kit followed by the CTAB protocol. Thirty‐three microsatellite (Simple Sequence Repeat – SSR) primer pairs were used to assay genetic variation. DNA amplification was carried out using a thermal cycler and PCR products were subjected to fragment analysis by capillary electrophoresis. Descriptive statistics and basic inferential statistical analyses were performed to access the variation of agro-morphological characters among rice varieties. Data were subjected to cluster analysis (CA) to examine the grouping tendencies and supplemented with Multidimensional scaling (MDS) to explore the procedural differences in the outcome. CA and MDS produced seven (07) groups which were further analyzed using Classification and Regression Analysis (CART) to extract the diagnostic agro-morphological features. Based on CART result, groups of rice varieties were characterized by lemma–palea color, presence or absence of awn, seedling height, and flag-leaf angle. Traditional rice accessions/varieties represent distant clusters on agro-morphological features. Molecular analyses revealed, all 33 loci displayed polymorphism (66.7-96.9 %) among 100 traditional rice accessions/varieties with a total of 387 alleles identified with an average of 11.72 alleles per accession. AMOVA results showed that 34% of the variation distributed among accessions/varieties, 59% of among individuals and 7% within individual indicating a comparatively high level of genetic differentiation among individuals of selected rice accessions/varieties. Structure analysis results illustrated that all 100 accessions/varieties were genetically structured into fifteen well-separated groups, high ΔK peak was recorded at K=15, K= 5, K= 19 and K= 2 respectively. UPGMA analysis based on Jaccard's similarity separated the accessions into five (5) major clusters. A cophenetic correlation with r=0.786 strongly supported the clustering pattern of UPGMA dendrogram. A principal coordinate analysis (PCoA) also confirmed the UPGMA clusters. The genetic diversity information obtained will be useful in efficient use of Sri Lankan rice germplasm collection in breeding programmes. This information will also be useful in management of in situ and ex situ germplasm collections in conservation programs for traditional rice varieties.

Electron-microscopic analyses on high-temperature fatigue crack growth mechanism in a Ni-based single crystal superalloy

The microscopic mechanism of high temperature (900 °C) fatigue crack growth in a single crystal Ni-based superalloy is investigated. Particular attention is focused to its relation to the cyclic misorientation markings (CMMs), formerly termed EBSD (electron backscattered diffraction) striation, left along the crack wake. Observation of a cross-sectioned crack tip is conducted by various electron microscopy i.e. SEM, EBSD, high-voltage TEM and STEM-EDS. A {100} fatigue crack subjected to a relatively high ΔK (40 MPam1/2) shows CMMs with an interval corresponding to crack growth rate (2–4 μm/cycle), consisting of heavily dislocated γ (Ni) phase and less dislocated γ’ (Ni3Al) phase. It is also revealed that local oxidation along the γ/γ’ interface at the crack tip existed at the current temperature/ΔK level. On the bases of these findings, a rational yet qualitative crack growth model that incorporated both brittle/ductile processes is proposed.

Distinct fatigue limit of a 6XXX series aluminum alloy in relation to crack tip strain-aging

In this study, a conventional precipitation-hardened A6061-T6 alloy (base alloy) and a modified alloy containing excess solute magnesium (Mg) compared to the base alloy were compared in terms of high-cycle fatigue property. Particular attention was paid to the emergence of a distinct knee point on the fatigue life diagram together with a time-dependent strengthening (coaxing) effect in the modified alloy under various test conditions. An attempt using specimens with different defect size successfully revealed that a distinct knee, which was absent in the base alloy, was attributed to the threshold against small crack growth. The clear coaxing effect in the modified alloy was also explicitly confirmed in terms of the high ΔK value achieved by the arrested cracks regardless of the defect size. The comparative tests conducted under different environments and temperature conditions further confirmed that the crack tip strengthening, essentially caused by the strain-aging capability endowed to the modified alloy, operated most prominently in the ambient air at room temperature. Such results were rationally interpreted by incorporating a competitive interaction of solute Mg and hydrogen (H) with dislocations at the crack tip.

Fracture mechanics behavior of TiNbSn alloys as a function of alloy content, cold working and aging

Mechanical properties such as tensile strength, ductility and elastic modulus, which are directly related to fracture mechanics characteristics, can be controlled during termo-mechanical manufacture of TiNbSn alloys. Cold working the alloys reduces its ductility and elastic modulus. Aging reduces their ductility further, but increases their elastic modulus. The present study aims to evaluate the effect of Nb (35% and 42% wt.) and Sn (0% and 2.5% wt.) contents on fracture toughness and fatigue crack growth of TiNbSn alloys of both cold worked and aged at 400 °C. The fracture toughness KIC was performed, and fracture analysis allowed to evaluate micromechanics changes. Crack growth rate(da/dN–ΔK) tests were also performed. Aging was beneficial to fracture threshold ΔKth and crack growth rate of the alloys. However, aging did not interfere with fracture toughness KIC. The increase in Nb content is beneficial to both fracture toughness and crack growth rate of the aged alloys. The addition of Sn in the aged 42% Nb alloy decreases the crack growth rate at higher ΔK. For alloys of similar elastic modulus, the size of dimples is proportional to fracture toughness.

Effects of surface oxide layer on fatigue crack propagation properties of submicrometre-thick freestanding copper films

To investigate the effects of oxide layer on fatigue crack propagation properties, fatigue tests in about 500-nm-thick copper films with a thickness-controlled oxide layer and without an oxide layer were conducted. Specimens with native oxide layer with a thickness of about 2 nm, those with thermal oxide layer with a thickness of about 20 nm and those without oxide layer were prepared. The results showed that fatigue crack propagation rate (da/dN) of specimens with thermal oxide layer was faster than of specimens with native oxide layer and without an oxide layer in higher ΔK and was smaller in lower ΔK.

Non-mono-exponential diffusion models for assessing early response of liver metastases to chemotherapy in colorectal Cancer

BackgroundPreoperative chemotherapy is becoming standard therapy for liver metastasis from colorectal cancer, so early assessment of treatment response is crucial to make a reasonable therapeutic regimen and avoid overtreatment, especially for patients with severe side effects. The role of three non-mono-exponential diffusion models, such as the kurtosis model, the stretched exponential model and the statistical model, were explored in this study to early assess the response to chemotherapy in patients with liver metastasis from colorectal cancer.MethodsThirty-three patients diagnosed as colorectal liver metastasis were evaluated in this study. Diffusion-weighted images with b values (0, 200, 500, 1000, 1500, 2000 s/mm2) were acquired at 3.0 T. The parameters (ADCk, K, DDC,α, Dsand σ) were derived from three non-mono-exponential models (the kurtosis, stretched exponential and statistical models) as well as their corresponding percentage changes before and after chemotherapy. The difference in above parameters between the response and non-response groups were analyzed with independent-samples T-test (normality) and Mann–Whitney U-test (non-normality). Meanwhile, receiver operating characteristic curve (ROC) analyses were performed to assess the response to chemotherapy.ResultsSignificantly lower values of K (the kurtosis coefficient derived from the kurtosis model) and σ (the width of diffusion coefficient distribution in the statistical model) (P < 0.05) were observed in the respond group before treatment, as well as higher ΔK and Δσ values (P < 0.05) after the first cycle of chemotherapy were also found compared with the non-respond group. ROC analyses showed the K value acquired before treatment had the highest diagnostic performance (0.746) in distinguishing responders from non-responders. Furthermore, the high sensitivity (100%) and accuracy (76.3%) from the K value before treatment was found in assessing the response of colorectal liver metastasis to chemotherapy.ConclusionsThe non-mono-exponential diffusion models may be able to predict early response to chemotherapy in patients with colorectal liver metastasis.

Mechanisms of fatigue crack propagation in a Q&P-processed steel

The fatigue crack propagation (FCP) behavior of a quenched and partitioned (Q&P), low-alloyed CSiCrMn steel containing 12% of retained austenite is investigated in ΔK-controlled tests at different R-ratios and compared with its quenched and tempered (QT) counterpart, containing 4% of retained austenite. Characteristic features of the crack wake and FCP surfaces are examined by scanning electron microscopy and related to the presence or absence of martensitic transformation. Comparing the FCP behavior of the Q&P condition with its QT counterpart, the fatigue threshold ΔKth is higher, and fatigue crack growth rates in the Paris-regime are lower, for Q&P. With an increase of ΔK, Paris-lines intersect and, at high ΔK, the fatigue crack growth resistance of the Q&P condition becomes inferior. Such FCG behavior is attributed to the amount and stability of retained austenite: at low ΔK, contributions of the martensitic transformation are negligible, and thus a higher fraction of retained austenite accounts for an increased FCG resistance. With increasing ΔK, an increasing percentage of retained austenite in the cyclic plastic zone at the crack tip is transformed, providing brittle pathways for fast crack propagation and thus lowering FCG resistance. Analysing the crack surface, cleavage-like intergranular crack propagation can be directly related to martensitic transformation: in the threshold region, FCP occurs predominantly in a transgranular mode and the percentage of cleavage planes increases as ΔK increases. This study is the first one that examines the FCP behavior in a Q&P-processed steel and one of very few which deal with the near-threshold FCP behavior in TRIP steels.