For tilt-rotor aircraft with coaxial rotors (coaxial rotor aircraft), reduction of radar cross section as well as acoustic noise can be essential for stealth design, and the rotation of the coaxial ...rotors can have an influence on noise and dynamic radar cross section (RCS) characteristics. In this paper, an approach to the prediction of both the sound pressure level (SPL) of noise and the dynamic RCS of coaxial-tilt aircraft is carried out, based on the theories of the FW-H equation, the physics optics method (PO) and the physical theory of diffraction (PTD) method. In order to deal with the rotating parts (mainly including coaxial rotors), a generated rotation matrix (GRM) is raised, aiming at giving a universal formula for the time-domain grid coordinate transformation of all kinds of rotation parts with arbitrary rotation centers and rotation axis directions. Moreover, a compass-scissors model (CSM) reflecting the phase characteristics of coaxial rotors is established, and a method of noise reduction and RCS reduction based on the phase modulation method is put forward in this paper. The simulation results show that with proper CSM parameter combinations, the reduction of noise SPL can reach approximately 3~15 dB and the reduction of dynamic RCS can reach 1.6 dBsm at most. The dynamic RCS and noise prediction and reduction method can be meaningful for the radar-acoustic stealth design of coaxial tilt-rotor aircrafts.
The development of quantum radar technology presents a challenge to stealth targets, so it is necessary to study the quantum detection probability. In this study, an analytical expression of the ...quantum radar cross section (QRCS) for complex targets is presented. Based on this QRCS expression, a calculation method for the detection probability for quantum radar is creatively proposed. Moreover, a self-designed flying-wing stealth aircraft is adopted to obtain the detection probability distributions of the conventional radar and the quantum radar in different directions. As revealed by the result of this study, the detection probabilities of the quantum radar and the conventional radar are significantly different, and the detection probability of the quantum radar has obvious advantages in most regions with a certain distance.
Abstract The technique of matrix acidification or acid fracturing is commonly utilized to establish communication with natural fractures during reservoir reconstruction. However, this process often ...encounters limitations due to filtration, which restricts the expansion of the primary acid-etching fracture. To address this issue, a computational model has been developed to simulate the expansion of an acid-etching wormhole by considering various factors such as formation process, injection duration, pressure build-up, and time-varying acid percolation rate. By analyzing the pumping displacement of acid-etching wormholes, this model provides valuable insights into the time-dependent quantities of acid percolation. It has been revealed that the filtration rate of acid-etching wormholes is strongly influenced by pumping displacement, viscosity, and concentration of the acid fluid used in stimulation as well as physical properties of the reservoir itself. Notably, viscosity plays a significant role in determining the effectiveness of acid fracturing especially in low-viscosity conditions. Acid concentration within 15% to 20% exhibits maximum impact on successful acid fracturing while concentrations below 15% or above 20% show no obvious effect. Furthermore, it was found that pumping displacement has a major influence on effective fracturing. However, beyond a certain threshold (> 5.0 m 3 /min), increased pumping displacement leads to slower etching distance for acids used in construction purposes. The simulation also provides real-time distribution analysis for acidity levels within eroded fractures during matrix-acidification processes and quantifies extent of chemical reactions between acids and rocks within these fractures thereby facilitating optimization efforts for design parameters related to matrix-acidification.
A cluster of acute respiratory illness, now known as Corona Virus Disease 2019 (COVID-19) caused by 2019 novel coronavirus (SARS-CoV-2), has become a global pandemic. Aged population with ...cardiovascular diseases are more likely be to infected with SARS-CoV-2 and result in more severe outcomes and elevated case-fatality rate. Meanwhile, cardiovascular diseases have a high prevalence in the middle-aged and elderly population. However, despite of several researches in COVID-19, cardiovascular implications related to it still remains largely unclear. Therefore, a specific analysis in regard to cardiovascular implications of COVID-19 patients is in great need.
In this single-centered, retrospective, observational study, 116 patients with laboratory-confirmed COVID-19 were enrolled, who admitted to the General Hospital of Central Theater Command (Wuhan, China) from January 20 to March 8, 2020. The demographic data, underlying comorbidities, clinical symptoms and signs, laboratory findings, chest computed tomography, treatment measures, and outcome data were collected from electronic medical records. Data were compared between non-severe and severe cases.
Of 116 hospitalized patients with COVID-19, the median age was 58.5 years (IQR, 47.0-69.0), and 36 (31.0%) were female. Hypertension (45 38.8%), diabetes (19 16.4%), and coronary heart disease (17 14.7%) were the most common coexisting conditions. Common symptoms included fever 99 (85.3%), dry cough (61 52.6%), fatigue (60 51.7%), dyspnea (52 44.8%), anorexia (50 43.1%), and chest discomfort (50 43.1%). Local and/or bilateral patchy shadowing were the typical radiological findings on chest computed tomography. Lymphopenia (lymphocyte count, 1.0 × 10
/L IQR, 0.7-1.3) was observed in 66 patients (56.9%), and elevated lactate dehydrogenase (245.5 U/L IQR, 194.3-319.8) in 69 patients (59.5%). Hypokalemia occurred in 24 (20.7%) patients. Compared with non-severe cases, severe cases were older (64.0 years IQR, 53.0-76.0 vs 56.0 years IQR, 37.0-64.0), more likely to have comorbidities (35 63.6% vs 24 39.3%), and more likely to develop acute cardiac injury (19 34.5% vs 4 6.6%), acute heart failure (18 32.7% vs 3 4.9%), and ARDS (20 36.4% vs 0 0%). During hospitalization, the prevalence of new onset hypertension was significantly higher in severe patients (55.2% vs 19.0%) than in non-severe ones.
In this single-centered, retrospective, observational study, we found that the infection of SARS-CoV-2 was more likely to occur in middle and aged population with cardiovascular comorbidities. Cardiovascular complications, including new onset hypertension and heart injury were common in severe patients with COVID-19. More detailed researches in cardiovascular involvement in COVID-19 are urgently needed to further understand the disease.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The stability of the surrounding rock is the key problem regarding the normal use of coal mine roadways, and the floor heave of roadways is one of the key factors that can restrict high-yield and ...high-efficiency mining. Based on the 1305 auxiliary transportation roadway geological conditions in the Dananhu No. 1 Coal Mine, Xinjiang, the mechanism of roadway floor heave was studied by field geological investigation, theoretical analysis, and numerical simulation. We think that the surrounding rock of the roadway presents asymmetrical shrinkage under the original support condition, and it is the extrusion flow type floor heave. The bottom without support and influence of mining are the important causes of floor heave. Therefore, the optimal support scheme is proposed and verified. The results show that the maximum damage depth of the roadway floor is 3.2 m, and the damage depth of the floor of roadway ribs is 3.05 m. The floor heave was decreased from 735 mm to 268 mm, and the force of the rib bolts was reduced from 309 kN to 90 kN after using the optimization supporting scheme. This scheme effectively alleviated the “squeeze” effect of the two ribs on the soft rock floor, and the surrounding rock system achieves long-term stability after optimized support. This provides scientific guidance for field safe mining.
Alternative polyadenylation plays an important role in cancer initiation and progression; however, current transcriptome-wide association studies mostly ignore alternative polyadenylation when ...identifying putative cancer susceptibility genes. Here, we perform a pan-cancer 3' untranslated region alternative polyadenylation transcriptome-wide association analysis by integrating 55 well-powered (n > 50,000) genome-wide association studies datasets across 22 major cancer types with alternative polyadenylation quantification from 23,955 RNA sequencing samples across 7,574 individuals. We find that genetic variants associated with alternative polyadenylation are co-localized with 28.57% of cancer loci and contribute a significant portion of cancer heritability. We further identify 642 significant cancer susceptibility genes predicted to modulate cancer risk via alternative polyadenylation, 62.46% of which have been overlooked by traditional expression- and splicing- studies. As proof of principle validation, we show that alternative alleles facilitate 3' untranslated region lengthening of CRLS1 gene leading to increased protein abundance and promoted proliferation of breast cancer cells. Together, our study highlights the significant role of alternative polyadenylation in discovering new cancer susceptibility genes and provides a strong foundational framework for enhancing our understanding of the etiology underlying human cancers.
On hot substrates with a temperature of 100 °C, the qualities of two-dimensional perovskite PEA
2
MA
2
Pb
3
I
10
(PEA = phenethylammonium, MA = methylammonium) films have been explored which are ...constructed with different spin-casting speeds. These films are performed at the speed of 1000, 2000, 4000, and 6000 revolution per minute (RPM). Below 4000 r, a higher RPM results in higher crystalline quality with more uniform morphology. Correspondingly, 4000 r devices show better performance on average (4.3% power conversion efficiency) and less hysteresis in the J-V curve than 1000 r (3.6%) and 2000 r devices (3.4%). However, for devices that were fabricated at 6000 r, inferior performance (2.8% on average) may not be predicted simply by the morphology characterization or optical measurement results at room temperature; instead, carrier trapping states can occur that result in thermally activated PL below 200 K with an activation energy of 18 meV, which do not occur in the 1000 r, 2000 r, and 4000 r films. Our results suggest that for evaluating 2D perovskite films prior to fabricating optimal devices, multiple morphology characterizations and optical measurements, including of low-temperature PL, will be helpful.
Graphical Abstract
Integrated PL intensity as a function of the inverse temperature of 1000 r, 2000 r, 4000 r and 6000 r, respectively, shows that optical measurements (especially low-temperature PL) are needed if we want to directly linked the optical properties of perovskite materials to the performances of corresponding devices.
Abstract
Silencing of endogenous retroviruses (ERVs) is largely mediated by repressive chromatin modifications H3K9me3 and DNA methylation. On ERVs, these modifications are mainly deposited by the ...histone methyltransferase
Setdb1
and by the maintenance DNA methyltransferase
Dnmt1
. Knock-out of either
Setdb1
or
Dnmt1
leads to ERV de-repression in various cell types. However, it is currently not known if H3K9me3 and DNA methylation depend on each other for ERV silencing. Here we show that conditional knock-out of
Setdb1
in mouse embryonic endoderm results in ERV de-repression in visceral endoderm (VE) descendants and does not occur in definitive endoderm (DE). Deletion of
Setdb1
in VE progenitors results in loss of H3K9me3 and reduced DNA methylation of
Intracisternal A-particle
(
IAP
) elements, consistent with up-regulation of this ERV family. In DE, loss of
Setdb1
does not affect H3K9me3 nor DNA methylation, suggesting
Setdb1
-independent pathways for maintaining these modifications. Importantly,
Dnmt1
knock-out results in
IAP
de-repression in both visceral and definitive endoderm cells, while H3K9me3 is unaltered. Thus, our data suggest a dominant role of DNA methylation over H3K9me3 for
IAP
silencing in endoderm cells. Our findings suggest that Setdb1-meditated H3K9me3 is not sufficient for
IAP
silencing, but rather critical for maintaining high DNA methylation.
To fully understand the factors influencing hydraulic fracture propagation in deep unconventional gas reservoirs, this study takes a block in China as an example. Firstly, a comprehensive geological ...mechanics model of the reservoir is constructed. From the perspectives of discrete natural fracture modeling, hydraulic fracture propagation analysis, and hydraulic fracturing numerical modeling, an analysis model of the influencing factors of hydraulic fracture propagation in the reservoir is established. This model is then used to conduct an analysis of the influencing factors, laying the foundation for optimizing fracturing design and improving fracturing effectiveness. The study shows that among factors such as cluster spacing, fluid intensity, natural fracture line density, and horizontal stress difference, cluster spacing has the greatest impact on hydraulic fracture propagation in the reservoir, followed by fluid intensity, while horizontal stress difference has the least impact. Under the condition of gradually increasing cluster spacing, the modified reservoir volume will initially increase and then decrease. As fluid intensity gradually increases, the modified reservoir volume will also increase, but due to economic constraints, fluid intensity should not be excessively high. When the natural fracture line density is low, the rate of increase in modified reservoir volume is relatively fast as it increases. However, when the natural fracture line density is high, the rate of increase in modified reservoir volume slows down as it continues to increase. As the horizontal principal stress difference gradually increases, the modified reservoir volume will gradually decrease.
Unmanned aerial helicopters (UAHs) have been widely used recently for reconnaissance operations and other risky missions. Meanwhile, the threats to UAHs have been becoming more and more serious, ...mainly from radar and flights. It is essential for a UAH to select a safe flight path, as well as proper flying attitudes, to evade detection operations, and the stealth abilities of the UAH can be helpful for this. In this paper, a stealth–distance dynamic weight Deep Q-Network (SDDW-DQN) algorithm is proposed for path planning in a UAH. Additionally, the dynamic weight is applied in the reward function, which can reflect the priorities of target distance and stealth in different flight states. For the path-planning simulation, the dynamic model of UAHs and the guidance model of flight are put forward, and the stealth model of UAHs, including the radar cross-section (RCS) and the infrared radiation (IR) intensity of UAHs, is established. The simulation results show that the SDDW-DQN algorithm can be helpful in the evasion by UAHs of radar detection and flight operations, and the dynamic weight can contribute to better path-planning results.