PS304 and Korolon™ 1350A foil bearing coatings were evaluated in startup/shutdown testing of compliant thrust pads against thrust runner disks. Tests were conducted at 540
°C, with pads loaded at a ...constant 3.44
kPa pressure while disk speed cycled between 0 and 19
m/s. As opposed to the case of uncoated Inconel X750 pads against uncoated Inconel 718 disks, PS304 disk coatings allowed hydrodynamic conditions to be more readily attained, as indicated by reduced speeds at which pad liftoff and touchdown occurred and lower coefficients of friction that existed at full speed. During low-speed portions of the cycle where direct sliding occurred, the PS304 disk coatings also lowered friction. PS304 disk coatings that were high-velocity oxyfuel (HVOF)-deposited attained these improved tribological performances following fewer required run-in cycles than those that were plasma-sprayed, as a result of lower attainable levels of as-finished roughness. HVOF deposition required reduced-size feed powder, with which PS304 disk coatings could be deposited using conventional propylene-fueled in addition to hydrogen-fueled HVOF systems. HVOF-deposited PS304 additionally possessed higher as-deposited strength than plasma-sprayed PS304. If instead the thrust pad was coated, with K1350A, even better hydrodynamic performance was attained with substantial further reductions in liftoff and touchdown speeds and coefficients of friction at full speed. When coupled with a PS304-coated disk the K1350A pad coating immediately provided this better hydrodynamic performance, with very few run-in cycles required before attainment. However, one drawback of K1350A pad coatings appeared to be an increased level of friction during low-speed sliding conditions where direct sliding contact with the disk occurred.
Aim
We report on our experience of elective subtotal colectomy and ileosigmoid anastomosis for colon cancer with focus on postoperative results, function and quality of life.
Method
Between 1998 and ...2011, 106 consecutive patients with colonic malignancy underwent this procedure electively. Function and quality of life (EORTC QLQ‐C30) were evaluated retrospectively with questionnaires sent to all patients free of recurrence.
Results
There were 62 men and 44 women (mean age 63 years). Postoperative mortality and morbidity rates were 1.9 and 26.4%, respectively. Persistent ileus was the main early complication (16%). After a mean follow‐up of 67 ± 36 months, 50 (78.1) out of 64 patients have been evaluated for function and quality of life. The mean number of bowel movements per 24 h was 3 ± 2 and significantly lower when the length of the remaining sigmoid colon was more than 15 cm (P = 0.049). Compared with a European reference population for EORTC QLQ‐C30 results, our patients had significantly more diarrhoea (26 vs 3, P = 0.0002) but less pain (10 vs 25, P < 0.0001) and better global quality of life (77 vs 62, P < 0.0001).
Conclusion
Elective subtotal colectomy for colon cancer is safe and associated with good function and quality of life. Ileosigmoid anastomosis should be discussed when extended colectomy is required, providing the rectosigmoid junction and its vascular supply can be oncologically preserved. For tumours located in the transverse colon or at the splenic flexure, this procedure may be the best surgical option.
Classical biological control programmes rely on mass production of high‐quality beneficial insects for subsequent releases into the field. Psyttalia lounsburyi (Silvestri) (Hymenoptera: Braconidae) ...is a koinobiont larval–pupal endoparasitoid of tephritid flies that is being reared to support a classical biological control programme for olive fruit fly in California. The mass‐rearing system for a P. lounsburyi colony, initiated with insects originally collected in Kenya, was evaluated with the goal of increasing production, while at the same time reducing time requirements for rearing in a quarantine facility. We tested the effect of exposure time of a factitious host Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), on parasitization, adult production, superparasitism, and sex ratio of P. lounsburyi and survival of the host. Parasitization rates were highest (31%) at 3‐ and 4‐hr exposure times, while adult production (i.e., emergence of wasp progeny) was highest (16%) at the 2‐hr exposure time. Superparasitism over the course of the study was 1.5% and did not appear to be a factor affecting parasitoid production. The sex ratio of wasp progeny was male‐biased and did not vary significantly over different exposure times. The rate of stings on host larvae increased with exposure time and was consistent with decreases in pupal eclosion from larvae and emergence rate of adult flies. When compared to current rearing procedures, the 2‐hr exposure time resulted in an overall 2.8‐fold increase in P. lounsburyi production when standardized for time.
Several members of the transforming growth factor-β (TGF-β) superfamily have been demonstrated to play regulatory roles in osteoblast differentiation and maturation, but the mechanisms by which they ...act on different cells at different developmental stages remain largely unknown. We studied the effects of TGF-β1 and bone morphogenetic protein-2 (BMP-2) on the differentiation/maturation of osteoblasts using the murine cell lines MC3T3-E1 and C3H10T1/2. BMP-2 induced or enhanced the expression of the osteoblast differentiation markers alkaline phosphatase (ALP) and osteocalcin (OC) in both cells. In contrast, TGF-β1 was not only unable to induce these markers, but it dramatically inhibited BMP-2-mediated OC gene expression and ALP activity. In addition, TGF-β1 inhibited the ability of BMP-2 to induce MC3T3-E1 mineralization. TGF-β1 did not sensibly modify the increase of Osf2/Cbfa1 gene expression mediated by BMP-2, thus demonstrating that the inhibitory effect of TGF-β1 on osteoblast differentiation/maturation mediated by BMP-2 was independent of Osf2/Cbfa1 gene expression. Finally, it is shown that TGF-β1 does not affect BMP-2-induced Smad1 transcriptional activity in the mesenchymal pluripotent cells studied herein. Our data indicate that in vitro BMP-2 and TGF-β1 exert opposite effects on osteoblast differentiation and maturation.
Oxide glasses exhibit slow crack growth under stress intensities below the fracture toughness in the presence of water vapor or liquid water. The log of crack velocity decreases linearly with ...decreasing stress intensity factor in Region I. For some glasses, at a lower stress intensity, Ko, log v asymptotically diminishes where there is no measurable crack growth. The same glasses exhibit static fatigue, or a decreasing strength for increasing static loading times, as cracks grow and stress intensity eventually reaches the fracture toughness. In this case, some glasses exhibit a low stress below which no fatigue/failure is observed. The absence of slow crack growth under a low stress intensity factor is called the fatigue limit. Currently, no satisfactory explanation exists for the origin of the fatigue limit. We show that the surface stress relaxation mechanism, which is promoted by molecular water diffusion near the glass surface, may be the origin of the fatigue limit. First, we hypothesize that the slowing down of slow crack growth takes place due to surface stress relaxation during slow crack growth near the static fatigue limit. The applied stress intensity becomes diminished by a shielding stress intensity due to relaxation of crack tip stresses, thus resulting in a reduced crack velocity. This diminishing stress intensity factor should result in a crack growth rate near the static fatigue limit that decreases in time. By performing Double Cantilever Beam crack growth measurements of a soda‐lime silicate glass, a decreasing crack growth rate was measured. These experimental observations indicate that surface stress relaxation is causing crack velocities to asymptotically become immeasurably small at the static fatigue limit. Since the surface stress relaxation was shown to take place for various oxide glasses, the mechanism for fatigue limit explained here should be applicable to various oxide glasses.
Surface shear stress relaxation of silica glass Aaldenberg, Emily M.; Aaldenberg, Jared S.; Blanchet, Thierry A. ...
Journal of the American Ceramic Society,
August 2019, 2019-08-00, 20190801, Volume:
102, Issue:
8
Journal Article
Peer reviewed
A constant angle of twist was applied to silica glass rods in order to produce a torsional shear strain and a reduction in torque representative of the stress state in the glass was measured as a ...function of time when rods were heat‐treated in air at temperatures, 550‐700°C, far below the glass transition temperature. The monotonic decrease of torque with time was explained by surface stress relaxation, which can be described by a relaxation of stress at the surface of glass which is promoted by water. The obtained surface stress relaxation diffusion coefficients were consistent with those obtained earlier from silica glass fiber bending under a similar water vapor pressure. The observed relaxation in torsion supports the mechanism of surface stress relaxation over the swelling‐based mechanism for applications including glass fiber strengthening.
5
µm thick CrN–Ag composite layers with 22
at.% Ag were deposited by reactive magnetron co-sputtering on 440C stainless steel substrates. Increasing the growth temperature from
T
s
=
500 to 600 to ...700
°C leads to Ag segregation within the CrN matrix and the formation of embedded lamellar Ag aggregates with increasing size, <
10
5, 9
×
10
6, and 7
×
10
7
nm
3, respectively. Ball-on-disk tests against 100Cr6 steel, followed by optical profilometry and energy dispersive spectroscopy, indicate that the Ag grains for
T
s
=
500
°C are too small to facilitate an effective lubricious surface layer, resulting in a friction coefficient
μ
=
0.58 and a composite coating wear rate of 3.8
×
10
−
6
mm
3/Nm that are nearly identical to those measured for pure CrN with
μ
=
0.64 and 3.6
×
10
−
6
mm
3/Nm. The
T
s
=
600
°C coating exhibits a Ag concentration which is 15% higher within than outside the wear track, and acts as a lubricious layer that reduces
μ to 0.47 and yields a 16× and 2.4× lower wear rate for coating and counterface, respectively.
T
s
=
700
°C leads to a dramatic increase in surface roughness and an associated increase in friction,
μ
=
0.85, and wear, 9.9
×
10
−
6
mm
3/Nm. Replacing the steel counterface with an alumina ball results in the lowest
μ
=
0.50 for
T
s
=
500
°C, attributed to the presence of Ag and the relatively low hardness of 16.5
GPa for this particular coating. In contrast, friction and wear increase dramatically for
T
s
=
600
°C, which is attributed to a breakdown of the lubricious Ag layer by the harder counterface. The transient friction coefficient μ
t during experiments with continuously increasing testing temperature
T
t
=
25–700
°C initially decreases for all samples, attributed to drying of the environment and an effective softening of both coating and counterface. For the
T
s
=
500
°C coating, a temperature activated solid lubricant transport yields a lubricious Ag surface layer and a very low
μ
t
=
0.05 at
T
t
~
500
°C. All coatings exhibit an increasing
μ
t for
T
t
>
500
°C, which is attributed to oxidative degradation.
The extended first-principles molecular dynamics (Extended FPMD) model introduced by Zhang et al. 2, based on an analytical single plane wave description of electronic orbitals for high energy ...electrons, has been implemented within the ab initio DFT software package Abinit and is now available. This model allows quantum simulations to be done smoothly on the full range of temperatures from cold condensed matter to hot dense plasmas passing through the warm dense matter regime which was currently not possible within the same ab initio model due to numerical limitations. In addition to presenting a brief theoretical background of the Zhang et al. method, we propose some improvements to the model. We then present the details of the implementation, and finally offer an application to the aluminum simulations for multiple densities, from room temperature to hot (thousands of eVs) temperature ranges, with a resulting Hugoniot equation of state that we compare with other methods.
Sodium for lithium and potassium for lithium ion‐exchanges of a lithium aluminosilicate glass were conducted and the resulting strength and dynamic fatigue characteristics were studied. Four‐point ...bend mechanical tests revealed that greater strengthening can be achieved by the potassium for lithium ion‐exchange, compared to the sodium for lithium ion‐exchange, and that the dynamic fatigue tendency is strongly suppressed by both exchanges. This suppression of dynamic fatigue characteristics of ion‐exchange strengthened glass was explained by the ability of the surface compressive layer to delay the onset of slow crack growth. Bulk stresses continue to increase in magnitude while the crack is arrested in the surface compressive stress region. Upon offsetting the surface compressive stress, the crack rapidly propagates into a high‐magnitude tensile stress field until the fracture toughness is reached, resulting in minimal crack growth prior to material failure. A slow crack growth model utilizing a fracture mechanics weight function was developed to simulate the experiments. Dynamic fatigue characteristics of the as‐received glass, without ion‐exchange treatment, were also measured and simulated for comparison.
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