53results about How to "Avoid short circuit current" patented technology

The invention relates to a method for realizing power distribution network closed loop and photovoltaic concentrated access by adopting flexible DC (direct current) power transmission. Two feeder lines are led out from each of two main transformers respectively and correspondingly; the four feeder lines are correspondingly connected to AC (alternating current) buses through connecting units respectively; in a flexible DC power transmission system, DC buses connected with DC boost ends of photovoltaic power generation modules are correspondingly arranged on two sides of a DC power transmission loop; during normal operation, the load, supplied by transformer substations, of the four feeder lines is smaller than or equal to 75% of the thermal stability limit power of a single feeder line, flexible DC converters in the flexible DC power transmission system operate as inverters, and the electric power sent out by the photovoltaic power generation modules are transmitted to 10 kilovolt feeder lines. According to the method, the power distribution reliability is high, the transformation is small, the comprehensive investment in inverters is reduced, and the method is suitable for an occasion with high requirement for power distribution reliability and needing grid connection of photovoltaic power stations.

The invention discloses an SEU (single event upset) / SET (single event transient)-resistant dynamic comparator, which comprises a pulse generating circuit based on a sensitive amplifier structure and an output latch circuit; the top of the whole comparator is provided with five input ports and four output ports outwards, the five input ports are respectively connected with clock signals, input signals and reference voltage signals, and the output ports are connected with data output signals; the pulse generating circuit is connected with the clock signals, the input signals, the reference voltage signals and the output latch circuit; and the output latch circuit is connected with the pulse generating circuit and the data output signals. The dynamic comparator has the advantages that the upset threshold LETth is greater than 500MeV / (mg.cm2); the time delay is reduced while the high-speed low power consumption of the SEU / SET-resistant dynamic comparator same as that of a traditional dynamic comparator is achieved; the symmetrical arrangement, equal time delay and same drive capacity of complementary output terminals Q and QB are realized; by adopting the sensitive amplifier structure, the clock network is simple, reliable and small in load; and by adopting the minor clock swing technology, the power consumption is obviously reduced.

The invention discloses a reclosure method involving a distributed generation power distribution network based on wide area information. The reclosure method aims at achieving the technical purpose of guaranteeing the power supply reliability of loads. The reclosure method includes the following steps that directional elements, a circuit breaker and a protector are arranged, reclosure operational motion is set, whether a distributed generation has the isolated island operation capacity or not is judged, and protection and reclosure are conducted. Compared with the prior art, the problem of asynchronous reclosure caused by DG upstream protection maloperation generated by adjacent feeder line faults is solved, operation of switching DG control strategies and splitting an isolated island generated when a DG downstream line breaks down in a reclosure front acceleration protection action mode is avoided, DG control method switching and the action cooperative relationship between reclosure and protection are achieved by fully utilizing the wide area information, the reclosure method can be suitable for the power distribution network with DG access, the DG power supply capacity is brought into full play, the power failure range is reduced, the power failure time is shortened, and the power supply reliability of loads is guaranteed.

The invention relates to a 110 kV substation protection and control action cooperation strategy suitable for DG (distributed generation) accessing. The strategy includes the procedures: main transformer high-tension side protection is modified and matched with 110kV incoming line upstream opposing side protection to form pilot protection used for removing incoming line failures; after the main transformer high-tension side protection acts, communication with an information processing center is made, and the information processing center performs analysis according to action information of main transformer low-tension protection and action information of the main transformer high-tension side protection; reclosure of the main transformer high-tension side protection is modified; the reclosure of the main transformer high-tension side protection and another protection cooperate in such a manner that the protection action is accelerated after the reclosure; the reclosure is started in such a manner that the protection action starts; action time of the reclosure is later than action time of reclosure of a 110kV incoming line. The strategy has the advantages that power outage range can be narrowed, power outage time is shortened, the ability of the DG to supply electricity is given to full play, and reliability of power supply for a load is guaranteed.

The present invention provides a charging system for an electric vehicle, capable of preventing generation of a short-circuit current even if short circuit occurs at a vehicle side charging lead. A charging system (10) for an electric vehicle (12) is arranged on vehicle side charging leads (46p, 46n) between a vehicle side charging connector (30) and an electrical storage device (24), and has a diode (32) for preventing a backflow current from the electrical storage device (24) to a charging device (14).

Provided is a starter motor control circuit capable of easily preventing the induction of a short-circuit current due to a ground fault in the power source line of a starter motor, in which a high current flows. A key switch (13) is connected with a battery (11), and a starter motor starting signal line (19) of a starter motor (18) is connected through a starter relay (16) with a start (ST) of the key switch (13). A protect relay (22) is disposed in a battery line (21) between the battery (11) and the starter motor (18). A ground fault detecting line (24) for detecting the ground fault of the battery line (21) is disposed between the battery line (21) and a controller (14). The controller (14) has a function to restrict the connecting actions of the starter relay (16) and the protect relay (22) when the ground fault of the battery line 21 is detected by a ground fault line (24), even if the key switch (13) is changed to the start (ST).

A converter utilizing synchronous rectification comprises a first switch, a second switch connected in series to the first switch, and a gate drive circuit controlling each switch to switch to on / off-state using pulse-width modulation. Each switch includes a channel region that is conductive in both forward and reverse directions in on-state and is not conductive in the forward direction in off-state, and a unipolar diode region conductive only in the reverse direction. The gate drive circuit synchronizes output timing for signal with which the first switch switches to on-state with output timing for signal with which the second switch switches to off-state, and synchronizes output timing for signal with which the first switch switches to off-state with output timing for signal with which the second switch switches to on-state.

The present invention discloses an output circuit that is able to adjust the output voltage slew rate and avoid short-circuit current, comprising: a control circuit for receiving an input data and generating a first set of control signals based on the input data; an output control device consisting of a first field effect transistor (FET) connected in series with a second field effect transistor (FET) and the point of connection is the output end for generating an output signal; a first capacitor having one end connected to a first working voltage and generates a first control voltage by charging / discharging on another end to control the gate of the first field effect transistor; a first switch for controlling charging / discharging of the first capacitor device based on the first set of control signals; a first current source for providing charging current for the first capacitor device; a second capacitor having one end connected to a second working voltage and generates a second control voltage by charging / discharging on another end to control the gate of the second field effect transistor; a second switch for controlling charging / discharging of the second capacitor device based on the first set of control signal; and a second current source providing charging current for the second capacitor device. The present invention adjusts output voltage slew rate of the output circuit by adjusting the time constant of the first and second capacitor devices.

The invention discloses an electrocatalytic oxidation device running under an ultrahigh voltage condition and a process method. The electrocatalytic oxidation device comprises a multi-stage serial spherical particle active electrode reaction device and a direct-current stabilized power supply device capable of generating ultrahigh voltage, wherein the interior of the multi-stage serial spherical particle active electrode reaction device contains a set of multi-stage serial spherical particle active electrode reaction system; particle electrodes are equidistantly fixed into A rows, B columns and C layers through positioning insulated plastic rods; a first spherical particle active electrode is connected with the positive electrode of the power supply device, and a (A*B*C)th spherical particle active electrode is connected with the negative electrode of the power supply device; a power-generating main body of the direct-current stabilized power supply device capable of generating the ultrahigh voltage is a rotor-type frictional electrifier; a rotating wheel of the electrifier is driven by a frequency-variable motor; the rotating speed rate of the rotor-type frictional electrifier is adjusted by controlling different rotating speeds of the motor; and output voltage is stabilized by a voltage-stabilizing device to obtain ultrahigh direct-current voltage of 2000-50000V.

The invention discloses a solar cell probe calibration method for a lunar dust measurement instrument. By using the solar cell probe calibration method, a solar cell probe can be calibrated on the ground; the method is simple and reliable and can provide basis for IOT (in orbit test) of the lunar dust measurement instrument. According to the solar cell probe calibration method, a solar cell shading effect principle is utilized and the solar cell probe is calibrated by establishing a ground calibration device, simulating sunlight irradiation and lunar dust deposition on the solar cell, measuring a relation between a short circuit current of the solar cell probe and a quantity of deposited lunar dust and testing influence of different sunlight incidence angles. By utilizing the calibration result, the lunar dust measurement instrument can calculate the quantity of the deposited lunar dust according to the sunlight incidence angle and the short circuit current of the solar cell probe in the testing process. The ground calibration device adopted by the invention has a simple structure and higher testing accuracy.

The invention discloses a doping method. The doping method includes the steps a doping layer is formed on a substrate in an ion injection mode; a dielectric layer is formed on the doping layer; annealing processing is carried out on the substrate with the dielectric layer; the dielectric layer is removed through cleaning fluids. After the doping layer is formed through ion injection, the dielectric layer is formed, and accordingly the performance of a PN structure can be improved, the dielectric layer can reduce doping concentration of the surface of the substrate and facilitate repair of lattice defects, the defect density in an injection damage layer can be obviously reduced, impurities on the substrate can be absorbed to a certain extent and accordingly influences of the harmful impurities are reduced.

Provided is a household cooking device. A power input part (1) connected with a commercial power source, a current fuse (2) and a load circuit (4) for controlling the cooking device are connected in series to form a closed circuit. A first surge protection device (3a) and a second surge protection device (3b) in serial connection are connected in parallel with a series circuit of the power input part (1) and the current fuse (2). The surge protection voltage of the first surge protection device (3a) and the surge protection voltage of the second surge protection device (3b) are respectively below the common maximum voltage inputted from the power input part (1).

The invention relates to a double-fed wind turbine stator current calculation method with the low penetration capacity. The method includes the steps that flux linkages of a stator and a rotor of a double-fed wind turbine are firstly calculated according to the running work condition of the double-fed wind turbine in the normal running steady state; then a power frequency component of the stator current is calculated through a sequence network equivalent circuit under the fault condition; flux linkage values of the stator and the rotor of the double-fed wind turbine under the fault steady-state condition are obtained through the adoption of calculation results of power frequency loops; the flux linkage values of the stator and the rotor in the normal steady state and the fault steady state are substituted into a controlled source expression of a rotating frequency current, and a rotating frequency component is calculated; finally, the power frequency component, the rotating frequency component and an attenuation alternating component of the stator current are added to obtain a final stator current analysis calculation result. By means of the double-fed wind turbine stator current calculation method, an analytical solution of the stator end current of the double-fed wind turbine can be given, trouble caused by a large amount of slow simulation calculation through a simulation platform is avoided accordingly, and on-site protection setting work is better done.

The invention relates to a method for manufacturing a nickel-based alloy plating layer. The method comprises the steps of polishing the inner wall of a sleeve, removing impurities and oxides, and wiping alcohol or acetone to remove oil stains; configuring welding equipment; configuring a welding rotary workbench, and fixing the sleeve to the welding rotary workbench; setting welding technological parameters; and conducting welding. The method is high in welding efficiency, high in welding seam quality, low in welding seam dilution rate and high in corrosion resistance. The invention further provides a processor and a medium. The processor is arranged on the welding equipment and used for executing instructions for manufacturing the nickel-based alloy plating layer. The medium is arranged in the processor and used for storing the instructions for manufacturing the nickel-based alloy plating layer. The processor and the medium are beneficial to achievement of automatic manufacturing of the nickel-based alloy plating layer.

The invention relates to a gate double-clamped IGBT device. The gate voltage clamping structure includes a third doped region located directly below the gate metal layer, a second doped region locatedin the third doped region, and a first doped region located in the second doped region. The first doping region is located in the first conductivity type drift region, the doping type of the first doping region is consistent with the doping type of the third doping region, and the doping type of the first doping region is different from the doping type of the second doping region. The first dopedregion is in ohmic contact with the gate metal layer, and the third doped region is in ohmic contact with the emitter metal. The invention has a compact structure, reduces the influence of the gate electrode of the IGBT device by the high peak of the positive and negative gate voltage, avoids the short-circuit current sharply increasing when the gate voltage is too high, and leads to the burnoutof the IGBT device, and is safe and reliable.

The invention discloses a hybrid latch applied to a multi-power supply system on chip. The multi-power supply system on chip is a system in which a main power supply and a plurality of branch power supplies are integrated on a working chip for synergetic power supply, and a working chip comprises a plurality of working circuits. The hybrid latch comprises a two-input nor gate, a two-input nand gate, a pull-up P-channel metal oxide semiconductor (PMOS) transistor, a pull-down N-channel metal oxide semiconductor (NMOS) transistor and a phase inverter, wherein the input end and the output end ofthe nor gate are connected with the input end and the output end of the nand gate; the other input end of the nor gate is connected with the main power supply; the other end of the nand gate is connected with the branch power supplies; the pull-up PMOS transistor and the pull-down NMOS transistor are connected with the output ends of the nor gate and the nand gate respectively; and the output endof the nor gate is connected with the phase inverter, so that a signal is output to a part of working circuits. When the branch power supplies are instable after the main power supply is electrified and becomes stable quickly, a connected working circuit can be switched off and short-circuit current of the working circuit disappears, so that the battery consumption of the multi-power supply system on chip can be lowered.

The positive pole piece comprises a current collector and first safety coatings correspondingly arranged on the two outer side surfaces of the current collector, positive active layers are arranged on the two outer side surfaces of the first safety coatings, and the positive active layers are made of ternary positive materials. Second safety coatings are arranged on the two outer side surfaces of the positive electrode active layer, and end face safety coatings are arranged on the side edge end faces, except the tab position, of the positive electrode piece. The invention also discloses a preparation method of the positive pole piece, which comprises the following steps: uniformly stirring the raw materials to prepare each layer of slurry, sequentially coating the slurry on the current collector, and then stamping and coating the end surface; the invention also discloses an application of the positive pole piece in a lithium ion battery. Through the three-layer coating structure of the positive pole piece, the electrical performance and the safety performance of the lithium ion battery are ensured at the same time; the multi-layer coating method is adopted, so that the preparation efficiency is high; the positive pole piece is used as a composition structure of the lithium ion battery, so that the needling safety performance of the lithium ion battery is improved.

The invention provides a transmission line switching combination scheme establishment method and device. The method is applied to the technical field of power systems, and comprises steps: an initialcut-off line number k and the maximum cut-off line number kmax are set; k-self impedance of each to-be-detected node after the k lines are cut off is calculated; according to k-self impedance of eachto-be-detected node, a k-line qualified scheme and a k-line unqualified scheme are determined; the initial cut-off line number k is added to k+d according to a preset step d; if k+d < / = kmax, a node in the k-line unqualified scheme is regarded as a to-be-detected node, and the step of calculating k-self impedance of each to-be-detected node after the k lines are cut off is returned; and if k+d > kmax or the current to-be-detected node set is empty, current line switching combination scheme establishment is determined to be completed. The transmission line switching combination scheme establishment method and the device provided by the invention can quickly establish a switching combination scheme.

A plasma display apparatus using a drive circuit. The drive circuit includes: first and second P-channel MOS transistors connected with a first voltage; a first N-channel MOS transistor connected between the first P-channel MOS transistor and a ground voltage, and having a gate connected with a first node and configured to receive a first input signal; and a second N-channel MOS transistor connected between the second P-channel MOS transistor and the ground voltage and having a gate connected with a second node and configured to receive a second input signal. An output P-channel MOS transistor is connected between the first voltage and an output node and has a gate connected with the second node, and an output N-channel MOS transistor is connected between the output node and the second voltage and has a gate supplied with an input signal having a same polarity as that of the first input signal. A P-channel MOS transistor has a source connected with the first node, a drain connected with the output node, and a gate connected with the second node.

The invention provides a voltage changer and a voltage changing system. A first circuit of the voltage changer outputs a common voltage on one of a first output end and a second output end according to an input signal and a received common voltage; a second current circuit conducts one, which does not receive the common voltage, of a third output end and a fourth output end to a second voltage according to a received triggering signal; and a switch circuit selects one of a third connection end and a fourth connection end to output the triggering signal according to the common voltage received by one of a first connection end and a second connection end and a bias voltage received by a bias voltage connection end so that a second current circuit coupled with the connection end outputting the triggering signal boosts the voltage of the output end which dose not output the common voltage to a second voltage. By using the voltage changer and the voltage changing system, the triggering signal restricts the conduction degree of the second current circuit, and the current drive capability can be enhanced with no need of increasing the distribution area, thereby effectively shortening the distribution area and reducing short-circuit current.

The invention discloses a baffling type ammonia-nitrogen wastewater advanced denitrification device and method. The device comprises a chlorine salt adjusting tank, an electrochlorination denitrification reaction tank and a pH adjusting tank which are connected sequentially, wherein chlorine salt can be added to the chlorine salt adjusting tank as required to adjust the concentration of chloride ions; baffling components are arranged in the electrochlorination denitrification reaction tank, the wastewater staying time can be prolonged, meanwhile, DSA polar plate groups are arranged, gaps amongpolar plates are filled with 3D particle electrodes, and the available chlorine production efficiency of an electrochlorination reactor can be enhanced. According to the electrochlorination advanceddenitrification device, by use of active chlorine produced by electrochlorination, ammonia nitrogen is finally oxidized into nitrogen to be removed, and no ammonium salt, nitrate or other byproducts can be produced; the continuous flow denitrification efficacy can be enhanced through the 3D electrodes and the baffling design of the electrochlorination denitrification reaction tank, advanced denitrification is realized, the operation is simple, and the problem of high ammonia-nitrogen content of effluent from the tail end of wastewater treatment can be solved.

The invention relates to cooking equipment. The cooking equipment comprises a first cooking machine with first heating elements and a second cooking machine with second heating elements, and each cooking machine is provided with a temperature sensor; an energy supply is used for supplying energy to the first electric heating elements and the second electric heating elements and controlled by a control system; the cooking equipment, a power input part connected with a power supply, a current fuse which cuts off a current when overcurrent flows, and a load circuit controlling the cooking equipment are connected in series to form a closed circuit, a first surge protective device and a second surge protective device which are connected in series are connected with the series circuit of the power input part and the current fuse in parallel, and surge protection voltage V1 of the first surge protective device and surge protection voltage V2 of the second surge protective device are below thegeneral maximum voltage input from the power input part. Accordingly, on the condition that too high surge protection voltage or surface current is applied, dish processing can be completed by replacing manual work.

The invention discloses a three dimension electrode reaction unit, which is characterized in that short flow of wastewater is avoided by arranging plate-type main electrodes placed in a parallel staggered manner, insulation baskets with holes and particle electrodes filled therein, aerator pipes, insulation frames of which the surfaces have fine wire screens, support pins and tees, so that the wastewater is more uniformly mixed and the retention time is simultaneously reduced; the aeration is more uniform, the degree of mixedness of the wastewater is deepened, and the mass transfer efficiency is greatly improved; the partitioning design of the particle electrodes can omit a discharge opening of a traditional device, so that loading and unloading of the particle electrodes are more convenient and cleaner, and the partitioning design of the particle electrodes also can block a short-circuit current difficult to overcome in a traditional three dimension electrode reaction unit, and economy, green and high efficiency are realized; a gas-liquid mixture can be removed while mixing and effluent discharging are performed; the occurrence of a siphon problem can be avoided; the height of the wastewater can be controlled through the length of a discharging tube, thus a basic parameter, namely the filling amount of the particle electrodes, is controlled, and a better treatment effect is further obtained.

The invention relates to a DC side auxiliary commutation hybrid converter topological structure and a control method thereof. The DC side auxiliary commutation hybrid converter topological structure comprises a three-phase six-bridge-arm circuit and an auxiliary commutation circuit which is connected in parallel with the DC side of the three-phase six-bridge-arm circuit and has forward current controllable turn-off and forward and reverse voltage blocking capabilities. The auxiliary commutation circuit is connected with a connection point of an upper bridge arm and a lower bridge arm of each phase of bridge arm circuit in the three-phase six-bridge-arm circuit through a two-way valve which is arranged on each phase of alternating current bus in a three-phase alternating current bus and hastwo-way opening and two-way voltage withstanding capabilities. According to the DC side auxiliary commutation hybrid converter topological structure and the control method thereof of the invention, the auxiliary commutation circuit connected in parallel with the direct current side of the three-phase six-bridge-arm circuit is additionally arranged in the hybrid converter topological structure, sothat the commutation fault problem of the hybrid converter topological structure can be solved, and the topological structure is simple to implement and low in cost.

The invention discloses a PV string optimizer system which comprises N PV string optimizers. Each PV string optimizer corresponds to a PV assembly string, and each PV assembly string is formed by connecting at least two PV assemblies in series. The input end of each PV string optimizer is independently connected with the output end of the corresponding PV assembly string for independent maximum power tracking. The PV string optimizers 1-N are connected to a DC / AC inverter through corresponding cables 1-N. The PV string optimizer system has the maximum power point tracking and short-circuit fault disconnection protection functions at the same time, each PV assembly string carries out independent MPPT tracking, and when any PV assembly string is short-circuited, the other PV assembly strings still work normally, the problem of parallel mismatch is avoided, and the situation that the whole loop continuously generates a short-circuit current under the condition that one PV assembly string has a short-circuit fault is avoided.

The invention relates to an apparatus for supplying electrical power to an electric motor, having a first controllable switching arrangement (101), which is designed to provide a first current path to the power supply in a first switching state and interrupt the first current path in a second switching state, having a second controllable switching arrangement (103), which is coupled to the first controllable switching arrangement and is designed to provide a second current path for current consumption in a first switching state and to interrupt the second current path in a second switching state, and having a control device (117) for changing the first controllable switching arrangement (101) and the second controllable arrangement (103) to the first switching state or to the second switching state, with the control device (117); being designed to change the second switching arrangement (103) to the first switching state when or after the first switching arrangement (101) is changed to the second switching state.

The invention discloses a hybrid latch applied to a multi-power supply system on chip. The multi-power supply system on chip is a system in which a main power supply and a plurality of branch power supplies are integrated on a working chip for synergetic power supply, and a working chip comprises a plurality of working circuits. The hybrid latch comprises a two-input nor gate, a two-input nand gate, a pull-up P-channel metal oxide semiconductor (PMOS) transistor, a pull-down N-channel metal oxide semiconductor (NMOS) transistor and a phase inverter, wherein the input end and the output end ofthe nor gate are connected with the input end and the output end of the nand gate; the other input end of the nor gate is connected with the main power supply; the other end of the nand gate is connected with the branch power supplies; the pull-up PMOS transistor and the pull-down NMOS transistor are connected with the output ends of the nor gate and the nand gate respectively; and the output endof the nor gate is connected with the phase inverter, so that a signal is output to a part of working circuits. When the branch power supplies are instable after the main power supply is electrified and becomes stable quickly, a connected working circuit can be switched off and short-circuit current of the working circuit disappears, so that the battery consumption of the multi-power supply system on chip can be lowered.

The invention provides a level shift circuit, an integrated circuit and electronic equipment. The level shift circuit comprises an input module used for outputting a first control signal according to a received first power supply voltage signal, a first input voltage, a second input voltage, an anti-phase voltage of the first input voltage and an anti-phase voltage of the second input voltage; the control voltage generation module is used for receiving the first control signal and generating a plurality of node voltages according to the first control signal and the second power supply voltage signal; the output control module is used for generating a first output signal, a second output signal, a third output signal and a fourth output signal according to the node voltage and a first power supply voltage signal; or a fifth output signal, a sixth output signal, a seventh output signal and an eighth output signal are generated according to the second power supply voltage signal and the node voltage.

The invention relates to a micromechanical z-axis inertial sensor (100), comprising: at least one first vibration mass element (10a); and-a torsion spring element (11a... 11n, 12a... 12n) connected to the first vibration mass element (10a); wherein-first torsion spring elements (11a... 11n) are each connected to the substrate (1), and second torsion spring elements (12a... 12n) are each connected to the first vibratory mass elements (10a); wherein-the first and the second torsion spring elements (11a... 11n, 12a... 12n) are each connected to one another by means of a lever element (13a... 13n), said lever element (13a... 13n) being designed to stop on a stop element (3a... 3n). The invention also relates to a method for producing a micromechanical z-axis inertial sensor (100).

The present invention relates to a submodule (1) for a converter in the high-voltage range with a reduced risk of cross-ignition. The submodule has a first and a second energy storage means (3, 4) which are connected in series, a first and a second semiconductor series circuit (13, 15) which are respectively connected in parallel with the first (3) and the second (4) energy storage means and which comprise a first (6) and a second (7), and respectively a third (9) and a fourth (10), power semiconductor switching unit which can be switched on and switched off, a first connection terminal (20) which is connected to a first potential point between the first and the second power semiconductor switching unit (6, 7), a second connection terminal (21) which is connected to a second potential point between the third and the fourth power semiconductor unit (9, 10). The invention proposes arranging a connecting switching unit (8) between the first and the second semiconductor series circuit (15), arranging a first connecting branch (14) with a first connecting branch diode (17) between the first potential point and the potential point between the energy storage means (3, 4), and arranging a second connecting branch (16) with a second connecting branch diode (18) between the second potential point and the potential point between the energy storage units (3, 4), wherein the connecting branch diodes (18, 19) are oriented in opposite directions to one another.