Main Pulse Research Articles

Year-round distribution of bearded seals, Erignathus barbatus, throughout the Alaskan Chukchi and northern Bering Sea

Bearded seals are pan-Arctic ice-obligate phocids; for the threatened Beringia population, the majority of the population feeds in the summer in the Chukchi Sea, then migrates south to overwinter in the northern Bering Sea. Contemporary information on the impact of rapidly changing climatic conditions on bearded seal distribution is essential for effective management. To monitor for marine mammals, passive acoustic recorders were deployed throughout the eastern Chukchi and northern Bering seas (64° N to 72° N), sampling at a rate of 16 kHz on a duty cycle of either 80 or 85 min every 5 h. Data from year-long deployments at nine sites over four years (2012–2016) were manually analyzed, totaling 13,275 days (∼75,000 h). Bearded seal calling activity was present at every site in every year. Calling activity increased from September through February and reached sustained and saturated levels from March through June, at which point calling ceased abruptly regardless of ice cover. The timing of calling and its abrupt cessation correspond with the known breeding season of bearded seals. However, the timing of the cessation of calling occurred earlier each year, corresponding with an earlier sea ice retreat. The sustained calling detected overwinter at all locations suggests that this is more than just a few animals that are remaining in the Chukchi Sea. Preceding this main pulse was a smaller peak in calling that progressed southward, corresponding with the fall migration of bearded seals to the Bering Sea. These results increase our knowledge on the year-round spatio-temporal distribution and migration patterns of this pagophilic species, and the relationship between calling activity and sea ice concentration.

Effects of Mantle Hybridization by Interaction with Slab Derived Melts in the Genesis of Alkaline Lavas across the Back-Arc Region of South Shetland Subduction System

AbstractLate Miocene to Late Pleistocene alkaline lavas in the northernmost part of the Antarctic Peninsula and its off-lying islands are the latest stage of magmatic activity that took place in response to lithospheric extension in the back-arc region of the South Shetland subduction system. The alkaline magmatism occurred much later than the main pulse of Cretaceous arc magmatism and generated basaltic extrusive rocks during several sub-aqueous/sub-glacial and sub-aerial eruption periods. The suite consists primarily of alkali olivine basalts with oceanic island basalt (OIB)-like trace element signatures, characterized by elevated highly to less incompatible element ratios compared to MORB. The samples have higher 87Sr/86Sr (0.70301–0.70365), and lower 143Nd/144Nd (0.51283–0.51294) and 176Hf/177Hf (0.28291–0.28298) than depleted MORB mantle. Their lead isotope ratios vary within a limited range with 206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb ratios of 18.797–18.953, 15.577–15.634, and 38.414–38.701, respectively. Sr, Nd, Hf and Pb isotope systematics suggest involvement of diverse source materials in the genesis of the alkaline magmas. Evaluation of radiogenic isotope and trace element data indicates that the source of the alkaline melts had a complex petrogenetic history, reflecting the effects of mantle hybridization along the slab mantle interface through interaction of mantle wedge peridotites with volatile-bearing, siliceous melts produced by melting of subducted sediments and basaltic oceanic crust. Hf-Nd isotope and trace element projections further demonstrate that the metasomatizing melt was likely generated by eclogite partial melting at sub-arc to post-arc depths, in equilibrium with a garnet-bearing residue and involved breakdown of high field strength elements (HFSE) retaining phases. Consumption of metasomatic amphibole during partial melting of hybridized peridotite at the wet solidus appears to have had a significant effect on the final melt compositions with high HFSE, Na and H2O contents.

Towards bright gamma-ray flash generation from tailored target irradiated by multi-petawatt laser

One of the remarkable phenomena in the laser-matter interaction is the extremely efficient energy transfer to gamma -photons, that appears as a collimated gamma -ray beam. For interactions of realistic laser pulses with matter, existence of an amplified spontaneous emission pedestal plays a crucial role, since it hits the target prior to the main pulse arrival, leading to a cloud of preplasma and drilling a narrow channel inside the target. These effects significantly alter the process of gamma -photon generation. Here, we study this process by importing the outcome of magnetohydrodynamic simulations of the pedestal-target interaction into particle-in-cell simulations for describing the gamma -photon generation. It is seen that target tailoring prior the laser-target interaction plays an important positive role, enhancing the efficiency of laser pulse coupling with the target, and generating high energy electron-positron pairs. It is expected that such a gamma -photon source will be actively used in various applications in nuclear photonics, material science and astrophysical processes modelling.

Place de l'IRM en cardiologie interventionnelle

Cardiovascular magnetic resonance has emerged as a very helpful tool for the interventional cardiologists not only in the assessment and treatment of coronary artery disease, but also in the evaluation of various structural cardiac diseases. The main pulse sequences are standardised, acquired during short breath-holds, and include steady-state free precession cines, dynamic myocardial first-pass perfusion imaging during contrast injection, and late enhancement imaging for the identification of myocardial substrates. Less than 30-minute CMR studies are now available for the most common clinical indications. More recently, T1 and T2 parametric myocardial maps are promising for detailed myocardial tissue characterisation (edema, replacement fibrosis, diffuse interstitial fibrosis). Technical aspects will not be addressed with particular emphasis on clinical applications.

Suppressing scattering-induced nanosecond pre-pulses in Ti:sapphire multi-pass amplifiers.

In this Letter, we experimentally investigate a new kind of nanosecond pre-pulse, which originates from the bidirectional scattering of crystals in traditional Ti:sapphire multi-pass amplifiers. The experimental results demonstrate that the intensity of scattering-induced pre-pulses is very sensitive to the scattering angle, and the delay time between the pre-pulse and the main pulse is an integer multiple of the light path in each pass of the amplifier. An optimized multi-pass amplifier configuration is proposed, for what is believed to be the first time, to suppress the scattering-induced pre-pulses. The contrast ratio between pre-pulses and the main pulse is enhanced by more than two orders of magnitude, reaching a level of 10-10. This novel multi-pass amplifier configuration is very simple and economical, and provides an effective solution for the temporal contrast enhancement in the nanosecond range.

Distribution and damage potential of pulse beetles, Callosobruchus spp. (Coleoptera: Bruchidae) in Sindh, Pakistan

Callosobruchus spp. are global serious pests of pulses. Therefore, two studies were carried out to determine their distribution in three ecological zones of the Sindh, Pakistan along with their damage potential to major pulses. Survey was conducted from Zone-one (Ghotki, Sukkur and Larkana districts), Zone-two (Hyderabad, Mirpur Khas and Shaheed Benazirabad districts) and Zone-three (Karachi district) during March – April 2020. Grain samples of main pulses i.e., chickpea (channa), field pea (matar), cowpea (lobia), green lentil (moong) and daal channa were collected from three locations of each district and brought to Stored Grain Research Laboratory, Department of Entomology, Faculty of Crop Protection, Sindh Agriculture University, Tandojam for further examination. Three pulse beetle species i.e., C. maculatus, C. chinensis and C. analis were identified from the collected pulse samples as the highest populations of adults, eggs, grubs and pupae was recorded from moong, followed by lobia and gram. No population of pulse beetle was recorded from daal channa and matar. Callosobruchus maculatus was the most dominant species at all sampling as higher beetle populations were recorded from Mirpur Khas and Sukkur districts. Therefore, both these strains were further evaluated for their feeding preference and weight loss assessment on various pulses i.e., gram (chickpea), lobia (cowpea), moong (green gram) and daal channa (yellow lentil) in no-choice under laboratory conditions. C. maculatus showed a significant feeding preference among pulses with lobia and gram being the most preferred, whereas daal channa was the least preferred, hence suffered highest and lowest weight loss, respectively. Therefore, proper storage and quarantine measures are suggested to be taken in the transportation and storage of pulses to restrict the spread and damage of pulse beetles.

Polarization attractors driven by vector soliton rain.

Soliton rain is a bunch of small soliton pulses slowly drifting near the main pulse having the period of a round trip. For Er-doped fiber laser mode-locked by carbon nanotubes, for the first time, we demonstrate both experimentally and theoretically a new type of polarization attractors controllable by vector soliton rain. With adjusting the pump power, vector soliton rain takes the form of pulses with rotating states of polarization which enable transforming slowly evolving trajectories on the Poincaré sphere from the double-scroll spiral to the circle. The obtained results on controlling complex multisoliton dynamics can be of interest in laser physics and engineering with potential applications in spectroscopy, metrology, and biomedical diagnostics.

A re-evaluation of the Meso-Cenozoic thermo-tectonic evolution of Bogda Shan (Tian Shan, NW China) based on new basement and detrital apatite fission track thermochronology

ABSTRACT Bogda Shan is a mountain belt located at the eastern extremity of the Chinese Tianshan and records a complex and debated exhumation history. Previous studies have reported a young Cenozoic thermal history for the exhumation of Bogda Shan, which is in conflict with the observation of preserved Mesozoic erosion surfaces in the area. This study re-evaluates the Meso-Cenozoic thermo-tectonic evolution of Bogda Shan using apatite fission track (AFT) thermochronology. Palaeozoic basement (meta-sandstone) samples collected from the northern and southwestern flanks of the mountain ranges reveal apparent Mesozoic AFT ages ranging from ~202 Ma to ~97 Ma. Inverse thermal history modelling results reveal slow to moderate basement cooling during the early Mesozoic, corresponding to relatively low levels of exhumation. This accounts for the preservation of low-relief Mesozoic peneplanation surfaces recognized at elevations of ~3500–4000 m. None of the presented AFT data and thermal history models show any evidence for significant deep Cenozoic exhumation. In the neighbouring Junggar Basin, a Middle Jurassic sandstone sample records partial resetting of the AFT system during the Cretaceous. This observation conflicts with previous data (from the same Jurassic strata) where complete resetting of the AFT clock during the Cenozoic was suggested. Furthermore, Lower Cretaceous and Palaeogene sediments from the Turpan-Hami Basin show non-reset detrital AFT age populations of ~197, ~135, and ~104 Ma, which are coincident with the main pulses of exhumation recorded in the Chinese North Tianshan. Based on a comprehensive summary of the published data, we argue for a Mesozoic building of the Bogda–Balikun–Harlik mountain chain in the eastern Chinese Tianshan. Subsequent Cenozoic exhumation must have been relatively modest at most (<2 km) as it was not recorded by AFT thermochronology.

Gradual warming prior to the end‐Permian mass extinction

AbstractThe biggest known mass extinction in the history of animal life occurred at the Permian–Triassic boundary and has often been linked to global warming. Previous studies have suggested that a geologically rapid (&lt;40 kyr) temperature increase of more than 10°C occurred simultaneously with the main extinction pulse. This hypothesis is challenged by geochemical and palaeontological data indicating profound environmental perturbations and a temperature rise prior to the main extinction. Using secondary ion mass spectrometry (SIMS), we measured oxygen isotope ratios from Changhsingian (late Permian) ostracods of north‐western Iran. Our data show that ambient seawater temperature began to rise at least 300 kyr prior to the main extinction event. Gradual warming by approximately 12°C was probably responsible for initial environmental degradation that eventually culminated in the global end‐Permian mass extinction.

LONG-TERM AFTERGLOW OF SOLID SCINTILLATORS.

Most of scintillators used for radiation detection exhibit afterglow, which is emission of light with longer decay times than that of main light pulse. High signal from afterglow has usually negative influence on detection parameters, e.g. for energy resolution in spectrometry measurements. The paper deals with long-term afterglow of some types of scintillators, which is more significant in the case of integral measurement when current in the photodetector is measured. The range of studied decay times was in the order of tens of seconds to days. Seven types of scintillators were measured: BGO, CaF2(Eu), CdWO4, CsI(Tl), LiI(Eu), NaI(Tl) and plastic scintillator. Excitation of scintillators was made using a UV lamp. After UV irradiation, a scintillator was inserted to scintillation detection unit and the anode current of photomultiplier tube was measured with a picoammeter. As results, CaF2(Eu) and plastic scintillator have relatively low long-term afterglow signal compared with other measured scintillators.

Study on the Weldability of Copper-304L Stainless Steel Dissimilar Joint Performed by Robotic Gas Tungsten Arc Welding.

The welding process of dissimilar metals, with distinct chemical, physical, thermal, and structural properties, needs to be studied and treated with special attention. The main objectives of this research were to investigate the weldability of the dissimilar joint made between the 99.95% Cu pipe and the 304L stainless steel plate by robotic Gas Tungsten Arc Welding (GTAW), without filler metal and without preheating of materials, and to find the optimum welding regime. Based on repeated adjustments of the main process parameters—welding speed, oscillation frequency, pulse frequency, main welding current, pulse current, and decrease time of welding current at the process end—it was determined the optimum process and, further, it was possible to carry out joints free of cracks and porosity, with full penetration, proper compactness, and sealing properties, that ensure safety in operating conditions. The microstructure analysis revealed the fusion zone as a multi-element alloy with preponderant participation of Cu that has resulted from mixing the non-ferrous elements and iron. Globular Cu- or Fe-rich compounds were developed during welding, being detected by Scanning Electron Microscope (SEM). Moreover, the Energy Dispersive X-ray Analysis (EDAX) recorded the existence of a narrow double mixing zone formed at the interface between the fusion zone and the 304L stainless steel that contains about 66 wt.% Fe, 18 wt.% Cr, 8 wt.% Cu, and 4 wt.% Ni. Due to the formation of Fe-, Cr-, and Ni-rich compounds, a hardness increase up to 127 HV0.2 was noticed in the fusion zone, in comparison with the copper material, where the average measured microhardness was 82 HV0.2. The optimization of the robotic welding regime was carried out sequentially, by adjusting the parameters values, and, further, by analyzing the effects of welding on the geometry and on the appearance of the weld bead. Finally, employing the optimum welding regime—14 cm/min welding speed, 125 A main current, 100 A pulse current, 2.84 Hz oscillation frequency, and 5 Hz pulse frequency—appropriate dissimilar joints, without imperfections, were achieved.

A new horseshoe crab from the Permian-Triassic transition of South China: Xiphosurids as key components of post-extinction trophic webs

The end-Permian mass extinction led to the disappearance of >81% of marine species and the collapse of marine ecosystems. Despite the progress made in recent years, the severity of the impact of the mass extinction upon some groups still remains unclear. Horseshoe crabs are a typical example among these groups. Here we report a new fossil horseshoe crab, Guangyuanolimulus shangsiensis gen. et sp. nov. from the Permian-Triassic transitional beds in South China, representing the earliest putative fossil record of Limulidae. The occurrence of horseshoe crabs during the Permian-Triassic transition indicates the existence of a trophic web containing at least three levels immediately after the main pulse of the end-Permian mass extinction. Horseshoe crabs might have played an important role as predators in marine communities during the Permian-Triassic transition and the earliest stage of recovery.

Single Pulse Dispersion Measure of the Crab Pulsar

We investigate the use of bright single pulses from the Crab pulsar to determine separately the dispersion measure (DM) for the Main Pulse and Interpulse components. We develop two approaches using cross-correlation functions (CCFs). The first method computes the CCF of the total intensity of each of the 64 frequency channels with a reference channel and converts the time lag of maximum correlation into a DM. The second method separately computes the CCF between every pair of channels for each individual bright pulse and extracts an average DM from the distribution of all channel-pair DMs. Both methods allow the determination of the DM with a relative uncertainty of better than 10−5 and provide robust estimates for the uncertainty of the best-fit value. We find differences in DM between the Main Pulse, the Low Frequency Interpulse, and the High Frequency Interpulse using both methods in a frequency range from 4 to 6 GHz. Earlier observations of the High Frequency Interpulse carried out by Hankins et al. (2016) resulted in DMHFIP–DMMP of 0.010 ± 0.016 pc cm−3. Our results indicate a DMHFIP–DMMP of 0.0127 ± 0.0011 pc cm−3 (with DMcomp being the DM value of the respective emission component), confirming earlier results with an independent method. During our studies we also find a relation between the brightness of single pulses in the High Frequency Interpulse and their DM. We also discuss the application of the developed methods on the identification of substructures in the case of Fast Radio Bursts.

Spectral Analysis of GRB 220426A: Another Case of a Thermally Dominated Burst

We report a very bright, long-duration gamma-ray burst (GRB), GRB 220426A, observed by the Fermi satellite. GRB 220426A, with a total duration of T 90 = 6 s, is composed of two main pulses and some subpeaks. The spectral analysis of this burst with a Band function reveals that both the time-integrated and the time-resolved spectra are very narrow with a high α ≳ 0.2 and low β ≲ −3.1. It is highly reminiscent of GRB 090902B, a special GRB with a photospheric emission identification. Then, we perform the spectral analysis of this burst based on nondissipated photospheric emission, which can be well modeled by a multicolor blackbody with a cutoff power-law distribution of the thermal temperature. The spectral fittings reveal that the photospheric emission can well describe the radiation spectrum of this burst. We conclude that this burst would be a second burst in the class of GRB 090902B observed by the Fermi satellite. We also discuss the physics of the photosphere and the origin of the high-energy component in GRB 220426A.

Vibrational courtship disruption of Nilaparvata lugens using artificial disruptive signals.

The brown planthopper (BPH), Nilaparvata lugens (Stål; Hemiptera: Delphacidae) is a piercing-sucking pest that causes serious damage to rice plants by sucking the phloem sap from the plants and transmitting viruses. During courtship, the BPH vibrates its abdomen to produce signals that are transmitted to rice plants through its legs. Male BPHs search, locate, and mate with female BPHs after they exchange courtship signals with each other. Currently, spraying chemical pesticides is still the primary method for controlling BPH populations in paddy fields, although this approach has led to severe environmental pollution. A physical control method based on BPH courtship disruption to reduce the mating rate is a promising strategy for cutting environmental pollution. To acquire effective courtship disruptive signals, we developed a vibration signal recording, monitoring, and playback system for BPHs. Using this system, BPH courtship signals and male competition signals were collected and analyzed to obtain their frequency spectra. Results show that the mean main vibration frequency of female courtship signals is 234 Hz and the mean pulse rate is 23 Hz. The mean main vibration and pulse frequencies of the male courtship signals are 255 Hz and 82 Hz, respectively. Besides, the mean main vibration frequency of the male competition signal is 281 Hz. Seven different forms and frequencies of artificial signals were played back to male BPHs, then the courtship and behavioral responses of male BPHs were analyzed. Results indicate that a pure tone of 225 Hz prevents the males from recognizing female courtship signals. The male reply rate fell from 95.6 to 33.3% and the mean reply delay time increased from 5.3 s to 9.1 s. The reply rates of the other six artificial signals ranged from 42.9 to 83.7%, and the mean reply delays were between 5.0 s and 9.3 s. Therefore, the courtship behavior of BPHs can be disrupted by using specific artificial disruptive signals.

ZnO Nanoparticle-Mediated Seed Priming Induces Biochemical and Antioxidant Changes in Chickpea to Alleviate Fusarium Wilt.

Chickpea (Cicer arietinum L.) is one of the main pulse crops of Pakistan. The yield of chickpea is affected by a variety of biotic and abiotic factors. Due to their environmentally friendly nature, different nanoparticles are being synthesized and applied to economically important crops. In the present study, Trichoderma harzianum has been used as a stabilizing and reducing agent for the mycosynthesis of zinc oxide nanoparticles (ZnO NPs). Before their application to control Fusarium wilt of chickpea, synthesized ZnO NPs were characterized. X-ray diffraction (XRD) analysis revealed the average size (13 nm) of ZnO NPs. Scanning electron microscopy (SEM) indicated their spherical structure, and energy dispersive X-ray analysis (EDX) confirmed the oxide formation of ZnO NPs. Transmission electron microscopy (TEM) described the size and shape of nanoparticles, and Fourier transform infrared (FTIR) spectroscopy displayed the presence of reducing and stabilizing chemical compounds (alcohol, carboxylic acid, amines, and alkyl halide). Successfully characterized ZnO NPs exhibited significant mycelial growth inhibition of Fusarium oxysporum, in vitro. In a greenhouse pot experiment, the priming of chickpea seeds with ZnO NPs significantly increased the antioxidant activity of germinated plants and they displayed 90% less disease incidence than the control. Seed priming with ZnO NPs helped plants to accumulate higher quantities of sugars, phenol, total proteins, and superoxide dismutase (SOD) to create resistance against wilt pathogen. These nanofungicides were produced in powder form and they can easily be transferred and used in the field to control Fusarium wilt of chickpea.

Molecular hydrogen from organic sources in geological systems

We have recently shown that molecular hydrogen generation from organic matter occurs at high maturity levels (vitrinite reflectance 3–5%) in Lower Cretaceous shales of the Songliao Basin. To evaluate and extend these implications to a wider range of source rock types and organofacies, we report on two Paleozoic maturity suites from Australia, namely the Permian Patchawarra Formation (fluviodeltaic; Type-III; Cooper Basin) and the middle Cambrian Arthur Creek Formation (marine; Type-II; Georgina Basin), and additional mature marine source rocks from Europe and the USA.It can be inferred from high resolution mass spectrometry that rapid growth of aromatic ring systems is the major pathway for the formation of thermogenic molecular hydrogen from all organic matter types. Extensive open system pyrolysis experiments indicate that the main generation pulse occurs in the vitrinite reflectance range 3.5–5.0%. Kinetic parameters were constructed by subtracting the hydrogen associated with hydrocarbon formation from total hydrogen in the open-system experiments via adjustment factors defined by the relative yields of CH4 and H2. A cumulative H2 potential of 20 mg/g TOC is found with maximum rates of generation that are sufficient for feeding the deep biosphere. Back of the envelope calculations indicate ∼3.5E+10 tonnes of in-place accessible H2 globally, which is an order of magnitude lower than in-place shale gas resource estimates. Regionally, inferred here for the Patchawarra Formation in the Nappamerri Trough (Cooper Basin), yields per unit rock volume resemble those of economic shale gas in the Barnett Shale, Fort Worth Basin, USA.Organic particles are, at the SEM-scale (>30 nm), barren of secondary porosity in the case of terrigenous samples at all maturity stages, but show sponge-like porosity in the investigated marine source rocks exhibiting vitrinite reflectance >∼2.0%. Presence of such meso- and macropores is crucial for H2 storage in marine shales, as microporosity (<2 nm) yielding sorptive storage space for H2, is usually much higher in mature terrigenous kerogens.

Nanoparticle-insertion scheme to decouple electron injection from laser evolution in laser wakefield acceleration

A localized nanoparticle insertion scheme is developed to decouple electron injection from laser evolution in laser wakefield acceleration. Here we report the experimental realization of a controllable electron injection by the nanoparticle insertion method into a plasma medium, where the injection position is localized within the short range of 100 μm. Nanoparticles were generated by the laser ablation process of a copper blade target using a 3-ns 532-nm laser pulse with fluence above 100 J/cm2. The produced electron bunches with a beam charge above 300 pC and divergence of around 12 mrad show the injection probability over 90% after optimizing the ablation laser energy and the temporal delay between the ablation and the main laser pulses. Since this nanoparticle insertion method can avoid the disturbing effects of electron injection process on laser evolution, the stable high-charge injection method can provide a suitable electron injector for multi-GeV electron sources from low-density plasmas.

Insight-HXMT Discovery of the Highest-energy CRSF from the First Galactic Ultraluminous X-Ray Pulsar Swift J0243.6+6124

The detection of cyclotron resonance scattering features (CRSFs) is the only way to directly and reliably measure the magnetic field near the surface of a neutron star (NS). The broad energy coverage and large collection area of Insight-HXMT in the hard X-ray band allowed us to detect the CRSF with the highest energy known to date, reaching about 146 keV during the 2017 outburst of the first galactic pulsing ultraluminous X-ray source (pULX) Swift J0243.6+6124. During this outburst, the CRSF was only prominent close to the peak luminosity of ∼2 × 1039 erg s−1, the highest to date in any of the Galactic pulsars. The CRSF is most significant in the spin-phase region corresponding to the main pulse of the pulse profile, and its centroid energy evolves with phase from 120 to 146 keV. We identify this feature as the fundamental CRSF because no spectral feature exists at 60–70 keV. This is the first unambiguous detection of an electron CRSF from an ULX. We also estimate a surface magnetic field of ∼1.6 × 1013 G for Swift J0243.6+6124. Considering that the dipole magnetic field strengths, inferred from several independent estimates of magnetosphere radius, are at least an order of magnitude lower than our measurement, we argue that the detection of the highest-energy CRSF reported here unambiguously proves the presence of multipole field components close to the surface of the neutron star. Such a scenario has previously been suggested for several pulsating ULXs, including Swift J0243.6+6124, and our result represents the first direct confirmation of this scenario.

Divergence of High-Order Harmonic Generation by a Convex Plasma Surface

The electron density profile on a plasma surface has a decisive influence on the mechanism and characteristics of the plasma high-order harmonic generation. When the pre-pulse has a similar spatial and temporal distribution as the main laser pulse, the plasma surface on the target will expand to form a convex profile of the similar size as the focal spot of the main pulse. We experimentally observed that the divergence of the harmonics generated by the relativistic laser light incident on a silica target has a saddle-shaped structure. The two-dimensional particle-in-cell simulation with convex plasma surfaces explains the experimental results very well and infers a 0.12λL plasma scale length around the center of the convex profile. Further, we qualitatively explained that the asymmetry of the saddle-shaped harmonic divergence is caused by oblique incidence.