No abstract

The bleed hole diameter, depth, and boundary layer thickness are key design parameters of a supersonic bleed system. The evolution trend of single-hole bleed flow coefficient with the ratio of boundary layer thickness to bleed hole diameter and the ratio of bleed hole depth to diameter is investigated by numerical simulations under choking and non-choking conditions. The results show that the subsonic leading edge of the circular hole and the subsonic part of the boundary layer are the main factors causing lateral flow of the bleed hole. The effect of diameter on bleed mass flow rate is due to the viscous effect which reduces the effective diameter. The larger the ratio of displacement thickness to bleed hole diameter, the more obvious the viscous effect is. The depth affects bleed flow rate by changing the opening and closing states of the separation zone. When a certain depth is reached, the development of the boundary layer reduces the effective captured stream tube and thus reduces the bleed mass flow rate. The main objective of the study is to obtain the physical mechanism of the bleed hole size parameters affecting the bleed mass flow rate, and to provide theoretical guidance for the selection of the size of bleed holes in the design of a porous arrays bleed system in hypersonic inlets.

No abstract

S. mitis/oralis has been previously reported in isolated cases of bacterial endocarditis and liver abscesses. Its presence in urine is generally considered a contaminant. A 66-year-old male patient was admitted to the hospital due to recurrent chest tightness and four-year history of exertional dyspnea. On the second day of admission, the patient presented with urgent and frequent urination, as well as dysuria. Both initial and subsequent urine cultures showed S. mitis/oralis infection, with polymorphonuclear leukocyte phagocytosis observed in the second sample. MALDI-TOF results confirmed the isolated strain as S. mitis/oralis. Drug susceptibility testing revealed multidrug resistance to penicillin, ceftriaxone, cefepime, levofloxacin, ofloxacin, and tetracycline, but sensitivity to quinupristin/dalfopristin, vancomycin, and linezolid. The clinician then prescribed vancomycin for anti-infective treatment, which proved effective.

On the basis of the geometric similarity between polygons and circles, a bleed rate model of a supersonic inviscid circular hole is first established through a gradual approximation by regular polygons. The bleed mass-flow rate depends on the parameters at the entrance. A supersonic inviscid bleed choking model is further established by using the inflow Mach number and the pressure ratio when the expansion wave is parallel to the entrance. For a depthless hole at Mach 2.0 and with a pressure ratio of 0.5, the difference of flow coefficient predicted by the present model to that of computational fluid dynamics is 1.4% under nonchoking conditions. Under choking conditions with a pressure ratio of 0.1, the difference is 3.1%. Furthermore, the influence of the boundary layer on the bleed mass-flow rate is transformed into the influence of the displacement thickness on the effective size of the bleed hole. Based on that, the viscous bleed rate model is established, which shows a maximum error of 7.7% for a depthless bleed hole over laminar flow at Mach 4.0 and Reynolds number 2.590 × 10 5 . Compared with the reported results of the full bleed hole, the difference of the bleed mass-flow rate predicted by the present model is 3.8%.

BackgroundStreptococcus agalactiae can produce CAMP factor, which can promote the β-hemolysin activity of Staphylococcus aureus, forming an arrow-shaped hemolysis enhancement zone at the intersection of the two bacterial species on a blood agar plate. This characteristic feature of Streptococcus agalactiae has led to the widespread use of the CAMP test as an identification method.MethodsVaginal/rectal swabs, collected from women at 35–37  weeks of pregnancy, were first inoculated into a selective enrichment broth media, then subcultured onto GBS chromogenic agar and 5% sheep blood agar sequentially. The VITEK-2 automatic identification system and MALDI-TOF MS were initially employed for identification, followed by the CAMP test. CAMP-negative strains underwent 16S rDNA and cfb gene sequence analysis, as well as bacterial multilocus sequence typing.ResultsA total of 190 strains were isolated, with 15 identified as CAMP-negative. Further 16S rDNA gene sequence analysis confirmed that all 15 strains were Streptococcus agalactiae. The MLST typing assay revealed that these 15 strains were of the ST862 type. The cfb gene was amplified and electrophoresed, but no specific fragments were found, indicating that these strains lack the CAMP factor due to cfb gene deletion. Antibiotic susceptibility tests demonstrated no resistance to penicillin, ampicillin, vancomycin and linezolid among the GBS strains. However, there are significant differences in resistance rates to tetracycline.ConclusionThis study found that 7.9% of GBS strains isolated from the vagina/rectum of pregnant women were CAMP-negative, suggesting that the CAMP test method or primers targeting the cfb gene should not be used as the sole presumptive test for GBS identification.