Shock compression and spallation of a low-cost cobalt-free medium-entropy alloy (MEA), Fe40Mn20Cr20Ni20 (at%), with a face-centered-cubic structure are investigated via plate impact experiments, to ...reveal its dynamic mechanical properties and corresponding microscopic deformation/damage mechanisms. The Hugoniot equation of state, yield strength, spall strength and pullback rate are obtained from free-surface velocity histories. Post-deformation samples are characterized with transmission electron microscopy, scanning electron microscopy and electron backscatter diffraction. The Fe40Mn20Cr20Ni20 MEA exhibits a good balance in spall strength and ductility (low pullback rate) at a relatively low cost, compared to several other types of medium/high entropy alloys and steels. At sufficiently high impact velocity (e.g., 500 ms−1 here), nanoscale deformation twinning becomes a key deformation mechanism for Fe40Mn20Cr20Ni20 MEA in addition to dislocation slip. During spallation, voids (i.e., damage) nucleate preferentially at grain boundary triple junctions, and grow isotropically with increasing loading. Owing to fine grains and strong plastic deformation capability of the Fe40Mn20Cr20Ni20 MEA, void coalescence is accomplished by intragranular shear deformation bands and cracks, which contributes to its high ductility.
•Hugoniot EOS of Fe40Mn20Cr20Ni20 is obtained.•Fe40Mn20Cr20Ni20 MEA exhibits good balance between spall strength and ductility.•Nanoscale deformation twinning occurs at high-velocity impact.•Voids nucleate at grain boundaries, and coalesce via intragranular fracture.
Hepatocellular carcinoma (HCC) is a leading cause of cancer death worldwide; its incidence is increasing in the United States. Depending on disease extent and underlying liver status, patients may be ...treated with local, locoregional, and/or systemic therapy. Recent data indicates that radiotherapy (RT) can play a meaningful role in the management of HCC. Here, we review published experiences using RT for HCC, including the use of radiosensitizers and stereotactic RT. We discuss methods for performing preclinical studies of RT for HCC and biomarkers of response. As a part of the HCC Working Group, an informal committee of the National Cancer Institute's Radiation Research Program, we suggest how RT should be implemented in the management of HCC and identify future directions for the study of RT in HCC.
Plate impact experiments are conducted on the carbon nanotube (CNT) reinforced 2024Al composite fabricated by flake powder metallurgy and hot extrusion, to investigate the effects of microstructural ...anisotropy on its dynamic deformation and damage, as well as the role of CNTs. Three loading directions are explored with the loading axis being parallel to the extrusion, transverse or normal direction. Free-surface velocity histories are measured to evaluate the mechanical properties and damage processes, including the Hugoniot elastic limit (HEL; ∼0.8 GPa) and dynamic spall strengths (1.4−1.9 GPa). Postmortem samples are characterized with synchrotron X-ray computed tomography and scanning electron microscopy. The microstructural anisotropy of the composite (in terms of the orientation of lamellar microstructures) has a negligible effect on HEL but induces an anisotropy in spall strengths; spall strength is the highest for loading along the extrusion direction, the long axis of the lamellar microstructures. CNTs appear to increase the spall strengths of the 2024Al matrix, in contrast to other reinforcing fibers/particles. The crack propagation direction and damage features can be correlated with collinear propagation of microcracks following the lamellar microstructures.
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•Plate impact of CNT-reinforced AMCs has been firstly investigated.•The spall strength of CNT/2024Al composite is ∼50% higher than that of 2024Al alloy.•Microstructural anisotropy has a momentous effect on spall strength and damage degree.•CNTs are pulled out slightly and fractured because of high strain rates involved.
•Penetration into gelatin at different projectile diameters and velocities is explored.•A general formula for penetration depth is derived based on nondimensional analysis.•The general formula is ...valid for a wide range of projectile diameters and velocities.•FEM simulations are in good agreement with experimental results.
Ballistic gelatin is widely used as a simulant of soft tissues, and its dynamic responses to high-speed projectile penetration are critical for understanding soft tissue damage, wound ballistics, and protection gear design. Here, we investigate penetration dynamics of spherical steel projectiles with different diameters into a ballistic gelatin at different incident velocities. The projectile diameter ranges from 1 mm to 5 mm, and the incident velocity, from 50 m s−1 to 400 m s−1. Penetration dynamics is captured with high-speed photography. A power-law relation is found between the maximum penetration depth and projectile kinetic energy at high incident velocities, but not at intermediate and low velocities. Nondimensional analysis is applied to the penetration depth; a general relation is established for nondimensional maximum penetration depth as a function of projectile density, projectile diameter and projectile incident velocity for low-, intermediate- and high-speed penetration, and this relation can accurately describe the experiments. The drag force of projectile is analyzed to explain the relation between projectile acceleration and velocity. In addition, a calibrated finite element model reproduces well experimental observations such as the maximum penetration depth and projectile trajectory.
The influence of second-phase boron particles (up to 0.15 wt%) on impact response of aluminum is investigated under high strain rate gas gun loading. The Hugoniot elastic limit (∼0.11 GPa) shows a ...negligible dependence on boron particle content up to 0.15 wt%. The second-phase particles reduce considerably spall strength of aluminum, and such reduction is more pronounced at high boron content. Spall strength undergoes a slight decrease at high impact velocities. Scanning electron microscopy and synchrotron X-ray computed tomography analyses indicate a competition between microvoid nucleation and microvoid growth. The damage features and spall strength characteristics can be attributed to the weak particle–matrix interface.
Helium bubble influence on the deformation of aluminum is investigated via simultaneous electron backscatter diffraction and digital image correlation (DIC) during in situ tensile and compressive ...tests. The majority of helium is generated through the transmutation reaction 10B(n, α)7Li under neutron irradiation, which is carried out at 40 ∘C to ∼0.3 dpa. The mesoscale deformation behaviors of aluminum matrix with and without helium bubbles are compared, and the interactions between helium bubbles and slip bands are analyzed. Helium bubbles along with other types of irradiation-induced defects (like dislocation loops and black dots) harden significantly the aluminum matrix around second-phase AlB2 particles. Slip bands cannot penetrate the areas with high-density irradiation-induced defects. They bypass such areas through cross slip, exhibiting slip band deflection. Transmission electron microscopy on irradiated materials after deformation reveals abundant helium bubbles, dislocations, dislocation loops and black dots around AlB2 particles, due to complex interactions between irradiation-induced defects with dislocations. Helium bubbles together with other types of irradiation-induced defects have pinning effects on dislocations, and pressurized helium bubbles may also punch out dislocation loops. The multiscale analyses demonstrate the helium bubble-dominated hardening.
Almost 1-2% of the human genome is located within 500 bp of either side of a transcription initiation site, whereas a far larger proportion (≈25%) is potentially transcribable by elongating RNA ...polymerases. This observation raises the question of how the genome is packaged into chromatin to allow start sites to be recognized by the regulatory machinery at the same time as transcription initiation, but not elongation, is blocked in the 25% of intragenic DNA. We developed a chromatin scanning technique called ChAP, coupling the chromatin immunoprecipitation assay with arbitrarily primed PCR, which allows for the rapid and unbiased comparison of histone modification patterns within the eukaryotic nucleus. Methylated lysine 4 (K4) and acetylated K9/14 of histone H3 were both highly localized to the 5′ regions of transcriptionally active human genes but were greatly decreased downstream of the start sites. Our results suggest that the large transcribed regions of human genes are maintained in a deacetylated conformation in regions read by elongating polymerase. Common models depicting widespread histone acetylation and K4 methylation throughout the transcribed unit do not therefore apply to the majority of human genes.
Plant steroid hormones, brassinosteroids (BRs), are perceived by the plasma membrane-localized leucine-rich-repeat-receptor kinase BRI1. Based on sequence similarity, we have identified three members ...of the BRI1 family, named BRL1, BRL2 and BRL3. BRL1 and BRL3, but not BRL2, encode functional BR receptors that bind brassinolide, the most active BR, with high affinity. In agreement, only BRL1 and BRL3 can rescue bri1 mutants when expressed under the control of the BRI1 promoter. While BRI1 is ubiquitously expressed in growing cells, the expression of BRL1 and BRL3 is restricted to non-overlapping subsets of vascular cells. Loss-of-function of brl1 causes abnormal phloem:xylem differentiation ratios and enhances the vascular defects of a weak bri1 mutant. bri1 brl1 brl3 triple mutants enhance bri1 dwarfism and also exhibit abnormal vascular differentiation. Thus, Arabidopsis contains a small number of BR receptors that have specific functions in cell growth and vascular differentiation.
CREB is a transcription factor that functions in glucose homeostasis, growth factor-dependent cell survival, and memory. In this study, we describe a role of CREB in human cancer. CREB overexpression ...is associated with increased risk of relapse and decreased event-free survival. CREB levels are elevated in blast cells from patients with acute myeloid leukemia. To understand the role of CREB in leukemogenesis, we studied the biological consequences of CREB overexpression in primary human leukemia cells, leukemia cell lines, and transgenic mice. Our results demonstrate that CREB promotes abnormal proliferation and survival of myeloid cells in vitro and in vivo through upregulation of specific target genes. Thus, we report that CREB is implicated in myeloid cell transformation.
The frequent silencing of tumor suppressor genes by altered cytosine methylation and chromatin structural changes makes this process an attractive target for epigenetic therapy. Here we show that ...zebularine, a stable DNA cytosine methylation inhibitor, is preferentially incorporated into DNA and exhibits greater cell growth inhibition and gene expression in cancer cell lines compared to normal fibroblasts. In addition, zebularine preferentially depleted DNA methyltransferase 1 (DNMT1) and induced expression of cancer-related antigen genes in cancer cells relative to normal fibroblasts. Our results demonstrate that zebularine can be selective toward cancer cells and may hold clinical promise as an anticancer therapy.
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