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Summary A new species of the genus Ficophagus was recovered from the syconia of Ficus annulata from Xishuangbanna, Yunnan province, China. It is described herein as Ficophagus annulatae n. sp. and is characterised by possessing the combined characters of a short PUS (9-18 μm or 0.3-0.6 VBD long), an excretory pore (EP) located at the level between stylet basal knobs and metacorpus, presence of crustaformeria, amoeboid sperm, three pairs of subventral papillae on the male tail (one pair just adcloacal (P2), one pair halfway between cloacal aperture and tail terminus (P3), and one pair near tail tip (P4)), rounded male tail tip without mucron, absence of gubernaculum and bow-shaped spicule with indistinct rostrum. Ficophagus annulatae n. sp. was differentiated from other sequenced species by the partial small subunit (SSU) rRNA gene and D2-D3 expansion segments of the large subunit (LSU) rRNA gene. Phylogenetic analysis with the LSU D2-D3 expansion segment sequence suggested that F. annulatae n. sp. is clustered in the same highly supported monophyletic clade with F. benjamina, F. curtipes and F. microcarpus. It differs morphologically from these species in EP position, spicule and uterus morphology, and some morphometric characters.

The ambient temperature affects the electron density in the laser-induced plasma, which is reflected as changes in the atomic spectral linewidths. A thermometry technique for the gas flow field under constant pressure is proposed.

Summary A new species of the genus Ficophagus was recovered from the syconia of Ficus variegata from Shenzhen, Guangdong province, China. It is described herein as Ficophagus giblindavisi n. sp. and is characterised by possessing the longest stylet in males (35.1-45.8 μm) and most lateral incisures (5) of all currently described species in the genus, a short PUS (8.4-11.4 μm or 0.3 VBD long), excretory pore situated at or posterior to the nerve ring, amoeboid sperm, three pairs of subventral papillae on the male tail, rounded male tail tip with a mucron, absence of gubernaculum and sickle-shaped spicules with a terminal cucullus. Ficophagus giblindavisi n. sp. was differentiated from other sequenced species by the partial small subunit (SSU) rRNA gene and D2-D3 expansion segments of the large subunit (LSU) rRNA gene. Phylogenetic analysis with the LSU D2-D3 expansion segment sequence suggested that F. giblindavisi n. sp. is clustered in the same highly supported monophyletic clade with F. auriculatae and F. fleckeri.

Summary A new nematode species was recovered from the syconia of Ficus semicordata from Xishuangbanna Tropical Botanical Garden, Yunnan Province, China. It is described herein as Martininema semicordatae n. sp. and is characterised by having the combined characters of a long post-vulval uterine sac, excretory pore located at nerve ring level, amoeboid sperm, three pairs of subventral papillae on the male tail, rounded male tail tip with mucron, absence of gubernaculum (= apophysis), and a recurved, rose-thorn-shaped spicule lacking a terminal cucullus. Martininema semicordatae n. sp. differs from other sequenced species by differences in the partial small subunit (SSU) rRNA gene and D2-D3 expansion segments of the large subunit (LSU) rRNA gene. Phylogenetic analysis with LSU D2-D3 expansion segment sequences suggested that M. semicordatae n. sp. is clustered in a highly supported monophyletic clade with M. guangzhouense, M. fistulosus and M. baculum, and shares a common ancestor with these three species.

Summary A new nematode species was recovered from the syconia of Ficus hirta var. roxburghii from Chaozhou, Guangdong, China. It is described herein as Ficophagus chaozhouensis n. sp. and is characterised by possessing the combined characters of a short post-uterine sac, excretory pore located near the head, amoeboid sperm, three pairs of subventral papillae on the male tail, rounded male tail tip with mucron (occasionally swollen), absence of gubernaculum (or apophysis), a blunt rosethorn-shaped spicule without a terminal cucullus, and a digitate rostrum with a broadly squared tip. Ficophagus chaozhouensis n. sp. was separated from other sequenced species by differences in the partial small subunit (SSU) rRNA gene and D2-D3 expansion segments of the large subunit (LSU) rRNA gene. Phylogenetic analysis with LSU D2-D3 expansion segment sequences suggested that F. chaozhouensis n. sp. is clustered in the same highly supported monophyletic clade with F. aculeata, F. maxima and F. yoponensis, and is sister to F. aculeata.

Femtosecond lasers have been used in combustion diagnostics. Based on the characteristics of femtosecond laser filamentation, many diagnostic techniques have been developed. Here, we propose a method, based on femtosecond laser filamentation, for equivalence ratio measurements in CH4/air gases. By measuring the spatially resolved spectra of the femtosecond laser-induced filament, we found that the variation of the equivalence ratio in the flow field would affect the spatial distribution of the emission intensity of femtosecond laser-induced filament. On this basis, the equivalence ratio was calibrated by using the relative spatial positions of N2 (337 nm) and C2 (516.5 nm) signals in the filament. This method overcomes the interference of local air disturbance, having lower measurement uncertainty.

Pulse repetition interval (PRI) is an important feature of distributed radar signals. PRI feature extraction and PRI sequence classification are meaningful in modern electronic warfare (EW). This article recommends applying the k-medoids algorithm and feedforward neural networks (FNN) to classify PRI sequences. The proposed approach first calculates the first-order difference of PRI sequences, then uses the k-medoids algorithm to cluster the elements in each PRI sequence and its difference vector, and extracts the centroids, and feeds the centroids into the FNN classifier to categorize the sequences. Simulation results show the proposed approach achieves excellent performance and has strong robustness.

Ammonia (NH3) has been identified as a potential hydrogen-carrier fuel with no carbon emissions. Non-intrusive in-situ NH3 diagnostic technique is of great interest. In this work, femtosecond two-photon laser-induced fluorescence (fs-TPLIF) was demonstrated in NH3/N2 mixtures to achieve NH3 measurements. A femtosecond laser at 305 nm was used for two-photon excitation of NH3 to its excited state (X–C′), and the subsequent fluorescence at ~565 nm from transition C′-A was detected. In addition, a detection limit of 730 ppm was achieved in NH3/N2 mixtures. Furthermore, one-dimensional single-shot images of NH3 were obtained in both laminar and turbulent flow fields. This work is the first attempt of fs-TPLIF for polyatomic molecular gases measurements, and the obtained results indicate that fs-TPLIF could be a promising tool for NH3 measurements.

Ammonia (NH3), which can be a hydrogen carrier, is a promising alternative to fossil fuels in the future carbon-free economy. In situ techniques feasible for the remote and non-intrusive detection of NH3 will provide strong support for developing clean NH3 combustion. Here, we demonstrated a femtosecond two-photon laser-induced fluorescence (fs-TPLIF) technique for interference-free in situ NH3 measurements in laminar premixed NH3/air flames. The two-head band of NH3 at ∼565 nm was observed, which verifies the feasibility of fs-TPLIF for NH3 measurements in a combustion environment. The single-shot NH3 fs-TPLIF images with efficient signal-to-noise ratios were obtained. The variation of the thickness of the reaction zone with the equivalence ratio of NH3 flames was also obtained. As a result of the broad line width of the femtosecond laser, the OH fluorescence was also observed together with the NH3 fluorescence. The potential of fs-TPLIF for simultaneous measurements of NH3 and OH with only one laser was analyzed. The laser power dependence of NH3 and NH emissions was investigated. The radial distributions of NH3, NH, and OH in the flame were also discussed. This work is the first attempt of fs-TPLIF for NH3 measurements in a combustion environment, and the results indicate that fs-TPLIF is a feasible tool for NH3 measurements in combustion diagnostics. (Less)

When adopting 5-axis machine to mill the parts, it is desired to avoid the drastic change of tool orientation for improving the kinematics performance of 5-axis machining while ensuring no machining interferences. For this purpose, a kinematics performance oriented smoothing method is proposed to plan the tool orientations, which is focused specifically on minimizing the angular accelerations imposed on the rotary axes of 5-axis machine. In this method, with several specified representative tool orientations (RTOs), two B-spline curves, which represent the displacements of the rotary axes, are used to join smoothly the RTOs together and then to determine the tool orientations at other areas. The solutions for the two B-spline curves are achieved by solving a least-square objective function which minimizes the angular accelerations of the rotary axes. To restricting simultaneously the interpolated tool orientations in the geometric feasible domains (GFDs) of tool motion, a simple alternate strategy of first smoothing the tool orientation and then checking the machining interference is developed so that tool orientation planning and its geometric constraints are decoupled and the complicated constraint optimization process of tool orientation can be greatly simplified. Since the proposed method works in the machine coordinate system (MCS), it can not only ensure the smooth motions of the rotary axes without the machining interferences, but also can generate directly the rotary axis orders. Finally, the proposed method is validated by the experiments.

Femtosecond (fs)-laser electronic-excitation tagging velocimetry (FLEET) in a nitrogen flow field using a 267 nm laser was performed under the condition of fs-laser filamentation. The filamentous properties and their effects on velocity measurements were investigated and were compared with those of an 800 nm fs-laser. The results show that the required energy of the 267 nm laser pulse is as low as hundreds of μJ, and this is beneficial for reducing the potential perturbations to the flow flied. The filaments induced by the 267 nm laser are longer and thinner than are those induced by the 800 nm laser, which enlarges the velocity measurements region, and a precision of 1.3% was achieved.

Summary A new nematode species was recovered from the syconia of Ficus auriculata-complex, including F. auriculata, F. oligodon and F. hainanensis, from Xishuangbanna Tropical Botanical Garden, China. It is described herein as Ficophagus auriculatae n. sp. and is characterised by possessing the combined characters of a short post-uterine sac, excretory pore located between the metacorpus and the stylet basal knobs, testis multi-reflexed, amoeboid sperm, three pairs of subventral papillae on male tail, rounded male tail tip without mucron, absence of gubernaculum (= apophysis) and sickle-shaped spicules with terminal cucullus. Ficophagus auriculatae n. sp. was differentiated from other sequenced species by the partial small subunit rRNA gene and D2-D3 expansion segments of the large subunit rRNA gene. Phylogenetic analysis with the above-mentioned sequences suggested that F. auriculatae n. sp. has a closer relationship with F. fleckeri in the same highly supported monophyletic clade than with the other sequenced Ficophagus and Schistonchus sensu lato species.

Summary A new nematode species was recovered from the syconia of Ficus curtipes from Xishuangbanna Tropical Botanical Garden, Yunnan, China. It is described herein as Ficophagus curtipes n. sp. and is differentiated from all currently described species in the genus by the possession of a spicule with a ventrally recurved tip (terminal barb). It is further characterised by possessing a short post-uterine sac, an ovoid spermatheca, presence of crustaformeria, excretory pore located near the head, amoeboid sperm, three pairs of subventral papillae on the male tail, rounded male tail tip without mucron, rose-thorn-shaped spicules without cucullus and absence of gubernaculum (= apophysis). Ficophagus curtipes n. sp. was differentiated from other sequenced species by the partial small subunit rRNA gene and D2-D3 expansion segments of the large subunit rRNA gene. Phylogenetic analyses suggested that F. curtipes n. sp. has a closer relationship with F. benjamina and F. microcarpus in the same highly supported monophyletic clade than to the other sequenced Ficophagus and Schistonchus s.l. species.

Femtosecond laser-induced plasma spectroscopy (FLIPS) was performed to achieve full-range mixture fraction measurements in non-reacting CH4/air flow fields. A femtosecond laser at 800 nm was used to generate a plasma channel with a uniform intensity distribution. Through measuring spatially resolved spectra and calibration, we found that the spectral intensity ratios of CH (431 nm)/N2 (337 nm), CH (431 nm)/N2 (357 nm), C2 (516.5 nm)/N2 (337 nm), C2 (516.5 nm)/N2 (357 nm) and CH (431 nm)/O (777 nm) could be used to realize mixture fraction measurements, and the first four intensity ratios can achieve full-range mixture fraction measurements. Furthermore, through quantitative analysis of the distribution along the plasma channel, we analyzed the one-dimensional measurement capability of FLIPS. The main advantages of FLIPS for mixture fraction measurements are one-dimensional quantitative measurement, full-range measurement, high spatial resolution and no Bremsstrahlung interference.

This paper presents an online optimal midcourse trajectory modification algorithm for the hypersonic interceptions based on the neighboring optimal control theory, which takes the current states deviations and the revised terminal constraints as inputs and generates the optimal control modifications. Firstly, the midcourse guidance for hypersonic interception is introduced as an optimal control problem, which is solved with the well-developed Gauss Pseudospectral Method (GPM) to generate a nominal trajectory that satisfies the first order optimality conditions. Secondly, the Neighboring Optimal Trajectory Existence Theory (NOTET) is given and the first order optimality equations are further differentiated to second order to acquire the control modifications. The perturbations of the terminal co-states are expressed with the current states perturbations and the revised terminal constraints by solving the second order equations and inversely integrating the perturbation dynamic equations. The optimality of the proposed algorithm is proved. Finally, five different interception scenarios are simulated and comparisons are made with particle swarm optimization (PSO) method and GPM. Simulation results reveal that the proposed method has the merits of high precision equivalent with GPM and better computing efficiency than PSO and GPM, which testifies the effectiveness and online application feasibility.

Hydrogen atoms are key species in combustion of hydrogen/hydrocarbon fuels. Interference-free detection of hydrogen atoms natively generated in flames using femtosecond laser-induced fluorescence (LIF) was investigated employing two colors, i.e., 243 nm and 486 nm, as excitation source: two-photon excitation followed by a relay one-photon excitation. This strategy was compared with another commonly adopted two-photon LIF strategy using 205 nm for excitation. The potential interferences were investigated, and a direct verification method was proposed to prove this strategy be interference-free, and imaging of hydrogen atoms natively generated in methane/air flames was achieved.

Single-shot imaging of methyl radical (CH3) in premixed methane/air flames is demonstrated using photofragmentation laser-induced fluorescence (PF-LIF) technique. A pump-probe strategy was adopted with the pump laser at 212.8 nm photolyzing CH3, and with the probe laser at 426.8 nm detecting the photolyzed CH (X2Π) fragments. Spatially resolved spectrograph of the PF-LIF signal from a stable laminar flame was recorded across the reaction zone to investigate potential interferences. The results indicate that the single-photon channel, CH3 + 212.8 nm → CH (X2Π) + H2, dominates the photofragmentation process. The CH2 radical was excluded from being an interfering precursor of the CH (X2Π) fragments owing to its relatively low concentration and small absorption cross section. Naturally present CH in the flame was identified as the main interference, but was conservatively estimated to account for only less than 4% of the total PF-LIF signal. Signal-to-noise ratio of around 10 was realized for single-shot imaging of natural CH3 in turbulent jet flames.

Laser-based diagnostic techniques are critical nonintrusive methods of measuring the in-situ temperature in combustion flow fields. Developing temperature measurement techniques with high accuracy and precision is of great significance for studying the combustion. At present, nanosecond (ns) lasers are commonly used in these methods. However, the researches based on femtosecond (fs) lasers are relatively few. Here, we develop a thermometry technique for combustion fields based on fs laser-induced filament. When the fs laser propagates in an optical medium, a long uniformly distributed plasma channel (also named filament) will be generated. The clamped intensity inside the filament is high enough to generate excited atoms/molecules through fs laser-induced photochemical reactions. Subsequently, the excited atoms/molecules release fluorescence signals. The length of the filament can be measured by imaging the fluorescence signal with an ICCD camera, which is evaluated by the full width at half maximum (FWHM) of the spatial distribution of the filament emission signal. Based on theoretical analysis, the experimental data of the filament length are fitted with a power function, and the result is satisfactory compared with the R-squared measure of goodness (R2) of 0.984. This indicates that the filament length is correlated well with the temperature of the combustion field. A monotonic quantitative relationship between the filament length and the temperature can be established by a calibration process, and then the temperature of the combustion field can be measured. When the temperature changes from 1630 to 2007 K, the length of the filament shortens by 38%. This indicates that the filament length is sensitive to the temperature of the flow field. When the temperature is 2007 K, the absolute uncertainty of the measurement is ±25 K, and the relative uncertainly is about 1.2%. The spatial resolution of the measurement system is 50 μm, which was determined by a USAF 1951 Target. Based on the spatial resolution, the measurement precision can arrive at 17 K. Although, at present, this temperature measurement technique based on femtosecond laser-induced filament is used only in laminar premixed flames, it has potential applications in temperature measurements ranging from room temperature to combustion temperatures.

This paper describes the capturability analysis concerning pure proportional navigation (PPN) guidance law for hypersonic interception. Using a modified polar coordinate, the expression of the three-dimensional (3D) relative kinematic model of the missile and target becomes simpler. Then, the capture conditions of PPN guidance law, which are sufficient and necessary conditions for hypersonic interception, are derived by using an auxiliary function. Finally, the simulation results indicate that smaller navigation constant and bigger speed ratio render a smaller capture region for intercepting high speed targets.

Femtosecond laser electronic excitation tagging (FLEET) is a molecular tagging velocimetry technique that can be applied in combustion flow fields, although detailed studies of its application in combustion are still needed. We report the applicability of FLEET in premixed CH4–air flames. We found that FLEET can be applied in all of the combustion areas (e.g., the unburned region, the burned region and the reaction zone). The FLEET signal in the unburned region is significantly higher than that in the burned region. This technique is suitable for both lean and rich CH4–air combustion flow fields and its performance in lean flames is better than that in rich flames.

We demonstrate a femtosecond two-photon laser-induced fluorescence (fs-TPLIF) technique for sensitive CO detection, using a 230 nm pulse of 9 µJ and 45 fs. The advantages of fs-TPLIF in excitation of molecular species were analyzed. Spectra of CO fs-TPLIF were recorded in stable laminar flames spatially resolved across the flame front. A hot band (1, n) together with the conventional band (0, n) of the B→A transitions were observed in the burned zone and attributed to the broadband nature of the fs excitation. The CO fs-TPLIF signal recorded across the focal point of the excitation beam shows a relatively flat intensity distribution despite of the steep laser intensity variation, which is beneficial for CO imaging in contrast to nanosecond and picosecond TPLIF. This phenomenon can be explained by photoionization, which over the short pulse duration dominates the population depletion of the excited B state due to the high peak power, but only contributes in total a negligible X state depletion due to the low pulse energy. Single-shot CO fs-TPLIF images in methane/air flames were recorded by imaging the broadband fluorescence. The results indicate that fs-TPLIF is a promising tool for CO imaging in flames.

Ammonia (NH3) is a sustainable fuel with excellent emission characteristics. Hence, it is important to develop diagnostic techniques for NH3 combustion. In this paper, femtosecond laser-induced plasma spectroscopy (FLIPS) was performed in premixed NH3/air flames. The plasma emission spectra induced by the femtosecond laser in the flame and the chemiluminescence spectra of the flame itself were both measured. Through calibration, we found that the spectral intensity ratio of NH (336 nm)/N2 (337 nm) could be used for equivalence ratio measurements in NH3 combustion flow fields. This work is the first attempt at using a femtosecond laser-based technique for NH3 combustion diagnostics.

The applications of femtosecond lasers to the diagnostics of combustion and flow field have recently attracted increasing interest. Many novel spectroscopic methods have been developed in obtaining non-intrusive measurements of temperature, velocity, and species concentrations with unprecedented possibilities. In this paper, several applications of femtosecond-laser-based incoherent techniques in the field of combustion diagnostics were reviewed, including two-photon femtosecond laser-induced fluorescence (fs-TPLIF), femtosecond laser-induced breakdown spectroscopy (fs-LIBS), filament-induced nonlinear spectroscopy (FINS), femtosecond laser-induced plasma spectroscopy (FLIPS), femtosecond laser electronic excitation tagging velocimetry (FLEET), femtosecond laser-induced cyano chemiluminescence (FLICC), and filamentary anemometry using femtosecond laser-extended electric discharge (FALED). Furthermore, prospects of the femtosecond-laser-based combustion diagnostic techniques in the future were analyzed and discussed to provide a reference for the relevant researchers.

We demonstrate the enhancement of femtosecond (fs) laser-induced filaments in air and nitrogen flow fields using a nanosecond (ns) laser. With the ns laser being imposed on the filaments, the length and the emission intensity of the filaments were largely increased. Temporally resolved spectra of the enhanced filaments were obtained. The results show that the ns laser enhanced the short-lifetime fluorescence of nitrogen, which comes from the transition processes of N2 +(B2Σu + - X2Σg +), N2(B3Пg - A3Σu +) and N2(C3Пu - B3Пg). However, it had little effect on the long-lifetime chemiluminescence, which mainly comes from reactions such as N2(A3Σu +) + N2(A3Σu +) → N2(X1Σg +, v = 0) + N2(B3Пg). A possible explanation of this phenomenon is given, and this phenomenon might have potential applications in instantaneous one-dimensional measurements of various species in gas flow fields.

Femtosecond laser-induced plasma spectroscopy for in situ ammonia (NH 3 ) measurements was demonstrated in NH 3 ∕N 2 mixtures. When a femtosecond laser at 800 nm was focused at the flow field, the parent NH 3 molecules would be photolyzed to generate electronics excited NH fragments, and then indirect measurements of NH 3 could be realized by detecting the NH fluorescence (A 3 Π − X 3 Σ − ) at 336 nm. A detection limit of 205 ppm was achieved. This work is the first attempt, to the best of our knowledge, for ammonia measurements with a femtosecond laser, and the results are useful for the development of ammonia diagnostics.

We demonstrate a non-contact spatiotemporally resolved comprehensive method for gas flow velocity field measurement: Filamentary Anemometry using femtosecond Laser-extended Electric Discharge (FALED). A faint thin plasma channel was generated in ambient air by focusing an 800-nm laser beam of 45 fs, which was used to ignite a pulsed electric discharge between two electrodes separated over 10 mm. The power supplier provided a maximum voltage up to 5 kV and was operated at a burst mode with a current duration of less than 20 ns and a pulse-to-pulse separation of 40 μs. The laser-guided thin filamentary discharge plasma column was blowing up perpendicularly by an air jet placed beneath in-between the two electrodes. Although the discharge pulse was short, the conductivity of the plasma channel was observed to sustain much longer, so that a sequence of discharge filaments was generated as the plasma channel being blown up by the jet flow. The sequential bright thin discharge filaments can be photographed using a household camera to calculate the flow velocity distribution of the jet flow. For a direct comparison, a flow field measurement using FLEET [Michael, Appl. Opt. 50, 5158 (2011)] was also performed. The results indicate that the FALED technique can provide instantaneous nonintrusive flow field velocity measurement with good accuracy. (Less)

We demonstrate a velocimetric technique based on femtosecond laser-induced cyano (CN) chemiluminescence (FLICC). High intensity emission originated from CN(B-X) fluorescence was observed in filaments generated by focusing a femtosecond laser in methane-seeded nitrogen gas flows. The emission is strong and can last for hundreds of microseconds with a proper methane concentration. FLICC was adopted for velocity measurements, and promising results were obtained for near-wall measurements.