Ultrahigh-temperature hafnium diboride ceramics with additions of 15 vol.% MoSi
2
or 15 vol.% SiC or a combined addition of 15 vol.% SiC and 5 vol.% WC were produced by hot pressing in the range ...1800–2000°C. The density of the produced composite ceramics was >98%. The components interacted in the hot pressing process to form new high-temperature phases (WB, MoB). The graine size of all structural elements did not exceed 5 μm. The maximum bending strength was reached by the HfB
2
–15 vol.% SiC–5 vol.% WC samples: 587 ± 25 MPa at room temperature and 535 ± 18 MPa at a test temperature of 1800°C, being associated with transcrystalline fracture of the ceramics. A three-layer oxide film formed: the upper layer was borosilicate glass with a HfSiO
4
interlayer, the middle layer was HfO
2
with B
2
O
3
–SiO
2
inclusions, and the lower layer consisted of hafnium oxide and inclusions of other oxides. The total thickness of the oxide film was ~50 μm for the material oxidized at 1600°C for 5 h and ~150 μm at 1500°C for 50 h. The highest oxidation resistance was acquired by the HfB
2
–15 vol.% MoSi
2
composite, where the oxidation rate did not exceed ~1 mg/cm
2
∙ h because a dense and homogeneous HfSiO
4
layer developed on the surface. However, the most corrosion-resistant zirconium diboride composite, ZrB
2
–15 vol.% MoSi
2
, showed an oxidation rate of ~2 mg/cm
2
∙ h. This high oxidation resistance of the hafnium diboride ceramics is explained by slower oxygen diffusion in HfO
2
and HfSiO
4
than in ZrO
2
and ZrSiO
4
, which is confirmed by mathematical modeling of the oxidation process.
Hot pressing was used to produce compact ceramic samples with the following composition (wt.%): 60 ZrB
2
+ 20 SiC + 20 (Al
2
O
3
+ 32 t-ZrO
2
). The tetragonal modification of zirconium oxide in the ...eutectic was stabilized by yttrium oxide. The porosity of the samples was 3–5%. The mechanical properties of the ceramics (hardness
HV
, fracture toughness
K
Ic
, tensile strength
δ
f
, compressive strength
Y
, grain-boundary strength
S
, and bending strength σ) were studied. Analysis of the microstructure and elemental composition of the phases revealed that a defect-free structure developed in the ZrB
2
-based composite through strong Van Der Waals adhesive interaction at the SiC–Al
2
O
3
interface, which increased the fracture toughness to 9.4 MPa ∙ m
1/2
. In turn, this increased the grain strength from 0.64 GPa for the basic composite to 3.46 GPa for the ZrB
2
–SiC composite with an oxide addition. An addition of Al
2
O
3
+ 32 wt.% t-ZrO
2
was introduced in sufficient quantities not only to reduce the fracture stress but also to promote plastic deformation of the material for high-temperature bending strength. Study of the oxidation process showed that the weight increment of the 60 wt.% ZrB
2
+ 20 wt.% SiC + 20 wt.% (Al
2
O
3
+ 32 wt.% t-ZrO
2
) sample at 1600°C for a holding time of 1 h was stabilized by dense oxide scale formed on the material, while the weight increment of the ZrB
2
+ 20 wt.% SiC sample and, consequently, the scale thickness increased monotonically. The scale that formed on the ZrB
2
+ 20 wt.% SiC samples with an addition of Al
2
O
3
+ 32 wt.% t-ZrO
2
consisted of an upper Al
2
SiO
5
-based layer 50 μm thick with ZrO
2
inclusions and a lower ZrO
2
-based layer up to 80 μm thick with Al
2
SiO
5
inclusions. The eutectic Al
2
O
3
+ 32 wt.% t-ZrO
2
oxide addition to the basic ZrB
2
–SiC system had higher oxidation resistance and thus prevented the diffusion of oxygen into the material.
PurposePlacental growth factor (PlGF) is a member of the VEGF family that plays an important role in experimental models of diabetic retinopathy and retinal neovascularization. We aimed to ...investigate whether vitreous levels of PlGF correlated with proliferative diabetic retinopathy (PDR) status, VEGF levels, and bevacizumab treatment. We also analysed PDR membranes to confirm the presence of the PlGF receptor, FLT1, in endothelial cells.MethodsThis was a case-control study: undiluted vitreous fluid samples were obtained from 28 active PDR patients without preoperative bevacizumab treatment, 21 active PDR patients with preoperative bevacizumab treatment, 18 inactive PDR patients, and 21 control patients. PlGF and VEGF levels in samples were determined by enzyme-linked immunosorbent assay. Immunohistochemistry for FLT1 was performed on human PDR membranes.ResultsCompared to control, vitreous PlGF levels were higher in both active PDR without bevacizumab (P<0.0001) and with bevacizumab (P<0.0001). There was no significant difference in PlGF between active PDR patients without and with bevacizumab (P=0.56). Compared to active PDR, PlGF levels were significantly reduced in inactive PDR (P=0.004). PlGF levels were highly correlated with VEGF levels in active PDR. VEGFR1 was expressed in endothelial cells in human PDR membranes.ConclusionThe strong correlation of PlGF levels with PDR disease status and expression of FLT1 in human PDR membranes suggest that PlGF has a pathogenic role in proliferative diabetic retinopathy. Therapeutic targeting of PlGF with agents like aflibercept may be beneficial.
The atmospheric deposition of polycyclic aromatic hydrocarbons (PAHs) was investigated in Hungary by analyzing a moss (
Hypnum cupressiforme) species as a bioindicator. In the autumn of 1997, samples ...were collected at 29 sites distributed across Hungary. The concentrations of total PAH at these sites were in the range of 0.1567–10.45×10
4 μg kg
−1 with a mean value of 1.87×10
4 μg kg
−1. More than 99% of the total PAHs atmospheric deposition were low molecular weight PAHs (up to 3 ring compounds). The total PAH values showed no correlation with metal concentrations. However, most of the sites in this region showed a positive linear relationship between PAHs levels and traffic volume (
r
2=0.83;
P<0.001) while no relationship existed between PAH levels and population (
r
2=0.01;
P>0.1). Atmospheric deposition of PAHs at different regions in Hungary may be due to incomplete combustion of fuel. The total concentrations of PAHs were compared to the PAH levels in vegetation samples collected from different regions around the world. The highest PAHs concentrations accumulated were found in
Hypnum cupressiforme than other vegetation species. A greater affinity for PAH compounds by
Hypnum cupressiforme than other moss species probably caused larger amounts of accumulation. A relationship between accumulations of PAH compounds in
Hypnum cupressiforme and octanol–air partition coefficients was obtained and is briefly discussed.
Dense composite ceramics based on B
4
C with an addition of 10 to 50 wt % of B
3
Si were obtained by hot pressing. An increased amount of boron silicide decreases the hot pressing temperature to ...obtain a high-density material. We found a hot pressing temperature, optimal for each of the compositions and possess the highest hardness, which is associated with the formation of a fine-grained structure. Densification occurs during reactive hot pressing, which consists in the decomposition of B
3
Si into Si and BSi
n
(
n
= 12–23) and further interaction with B
4
C to form SiC and B
12
(Si,B,C)
3
. The modification of boron carbide with silicon leads to the stabilization of hardness at ~24–26 GPa in the load range from 2 to 200 N. The highest bending strength of ~500 MPa is observed for samples with up to 20 wt % of B
3
Si. The optimal composition, which combines high values of hardness and flexural strength, is B
4
C–20 wt % B
3
Si.
Highlights • Electrosensory information is represented by multiple topographic maps in the ELL. • Short-term plasticity of synaptic feedback is matched to map-specific filtering. • Different synaptic ...dynamics across maps are best described by distinct mechanisms. • STP in feedback pathways contributes to functional specialization of the sensory maps.
To evaluate the clinical and genetic spectrum of inherited retinal diseases (IRDs) in a Kuwaiti tribe.
Forty four patients with IRDs from 28 nuclear families from the tribe, were evaluated for ...presenting symptoms, visual acuity, fundus examination, OCT, microperimetry, full-field (ff), and multifocal electroretinography (mERG) and genotyping.
Seventeen patients were diagnosed with autosomal recessive retinitis pigmentosa (arRP) associated with
c.606C>A with onset of nictalopia in the third decade, myopia, and macular atrophy by the age of 50; eleven with autosomal recessive cone/rod dystrophy or macular dystrophy associated with
c.606C>A (p.Asp202Glu) mutation with color and central vision deterioration in teenage, myopia, paracentral ring scotoma and macular atrophy; eleven were with arRP associated with
c.992 + 1 G > A mutation with onset around 5 years, myopia, cataract, retained central fixation, and ellipsoid zone and late perimacular atrophy; five-with Leber congenital amaurosis associated with homozygous
for c.1107delA mutation with extinguished ffERG and electrophysiological phenotype of rod and cone; and one patient-with autosomal recessive rod-cone dystrophy associated with homozygous
c.992 + 1 G > A, who was homozygous
c.5882 G > A and heterozygous
; c.2137 + 1 G > A.
This study represents a typical tribe from the Middle East with high rate of consanguinity for many generations that harbors multiple mutated genes associated with IRD. It demonstrates the predominant phenotype and its variability in retinal disorders caused by identical mutations and illustrates the nuances in the clinical presentation and disease progression of patients with pathogenic mutations in more than one gene.
Age-related macular degeneration (AMD) is a leading cause of visual impairment in aging populations in industrialized countries. Here we investigated whether the genotype of vascular endothelial ...growth factor A (VEGFA) gene is associated with response to anti-VEGF therapy. 223 eyes with neovascular AMD were treated with intravitreal anti-VEGF therapy. Responders were defined as patients who had an improvement in best corrected visual acuity (BCVA) of at least 5 letters or one line on the EDTRS visual acuity chart along with resolution of intraretinal or subretinal fluid over 12 months. Patients who did not meet the definition of responders were classified as poor-responders. The vision of responders (n = 148) improved while the vision of poor-responders (n = 75) worsened (P<0.001). Responders on average had a decrease in central foveal thickness (CFT), while poor-responders had an increase in CFT (P <0.001). Compared with the responder group, the poor-responder group had a higher frequency of the risk (T) allele (Allelic P = 0.019) and TT genotype (P = 0.002 under a recessive model) for the VEGFA-rs943080 polymorphism. VEGFA expression was 1.8-fold higher in cells with the VEGFA rs943080 TT genotype than in cells with the VEGFA rs943080 CC genotype (P = 0.012). Age, gender, smoking, diabetes mellitus, and hypertension did not play a significant role in treatment response, but BMI was found to be significantly different between responders and poorresponders (P = 0.033). In conclusion, we demonstrated a potential pharmacogenetic relationship between the VEGFA gene and treatment response to anti-VEGF therapy.The studies are registered at ClinicalTrials.gov under the identifiers NCT00474695 (http://clinicaltrials. gov/ct2/show/NCT00474695) and NCT01464723 (http://clinicaltrials.gov/ct2/show/NCT01464723).
We prepared dense high-entropy ceramic material (TiZrHfNbTa)C by hot pressing; the optimum hot-pressing temperature is 2000°C. At lower temperatures, zirconium oxides, hafnium oxides, and undissolved ...carbides were observed in the ceramic composition. The strength of the resulting ceramics at room temperature was 394 ± 72 MPa, at a temperature of 1600°С, it was 119 ± 31 MPa. For pure carbides, a significant drop in hardness was observed at an increased load on the indenter, while for (TiZrHfNbTa)C, hardness is retained under any load. To achieve the maximum hardness and strength of high-entropy ceramics (TiZrHfNbTa)C, the amount of ZrO
2
and HfO
2
in the composition of ceramics should be decreased with a simultaneous decrease in grain size by using submicrometer-scale powders and selecting proper technological modes of production.
PDF
