A direct current and alternating electric field superimposed preservation method

Abstract

This invention discloses a method for preserving fruits and vegetables by superimposing DC and alternating electric fields, relating to the field of fruit and vegetable preservation technology. It maintains a dynamic balance between two contradictory processes: inhibiting spoilage and maintaining the body's resilience. A physiological stress balance index is set to assess the balance between inhibition and activation effects within a complete cycle. The method integrates the temporal inhibition effect of the positive electric field and the temporal activation effect of the negative electric field to generate initial time-series parameters where the inhibition and activation effects reach dynamic equilibrium within a complete polarity cycle. This effectively delays spoilage while maintaining sufficient vitality to resist environmental stress, thus achieving excellent preservation results. Simultaneously, real-time collected physiological signals are compared with preset thresholds, and a decision on polarity switching or maintenance is output after logical judgment, giving the preservation strategy adaptive optimization capabilities and enabling precise responses to the actual state of the fruits and vegetables.

Description

Technical Field

[0001] This invention relates to the field of fruit and vegetable preservation technology, and in particular to a preservation method using a superposition of direct current and alternating electric fields. Background Technology

[0002] Postharvest preservation technology for fruits and vegetables is a crucial link in the agricultural product supply chain, reducing losses and enhancing value. Traditional preservation technologies mainly rely on low-temperature refrigeration and controlled atmosphere storage. Low-temperature technology delays spoilage by inhibiting the respiration of fruits and vegetables and the activity of microorganisms, while controlled atmosphere technology further enhances the preservation effect by adjusting the ratio of oxygen, carbon dioxide, and nitrogen in the storage environment. These technologies meet the needs of short-cycle circulation to a certain extent, but their preservation effect is still limited for agricultural products that require long-term storage or long-distance transportation. Physical field preservation technologies are gradually emerging, such as electrostatic field preservation and alternating electric field preservation technologies. Electrostatic fields mainly affect the cell membrane potential of fruits and vegetables and microbial metabolism through the action of electric field force, while alternating electric fields use their periodic changes to generate stronger disturbances to microorganisms.

[0003] The core drawback of existing superimposed electric field preservation technology is its static and unidirectional nature. Existing technologies mostly set fixed electric field parameters for specific fruits and vegetables, and rely on empirical settings, making it difficult to achieve ideal preservation results. The preservation effect is poor. At the same time, the static treatment mode cannot adapt to the continuous changes in the internal physiological state of fruits and vegetables as dynamic living organisms. In the early stage of storage, fruits and vegetables respire vigorously and spoilage factors are active, requiring a strong inhibitory electric field. In the middle and late stages of storage, fruits and vegetables enter the aging stage and need to maintain their resilience appropriately. A fixed polarity electric field cannot meet this dynamic demand, resulting in insufficient inhibition in the early stage or insufficient maintenance in the later stage. Summary of the Invention

[0004] In view of the aforementioned existing problems, the present invention is proposed.

[0005] Therefore, this invention provides a method for preserving food by superimposing DC and AC electric fields to solve the problem that parameter settings rely on experience and are static, resulting in poor preservation effects.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: In a first aspect, the present invention provides a method for preserving fruits and vegetables by superimposing DC and alternating electric fields, including: S1, for fruits and vegetables, presetting the basic parameter combination of superimposed electric fields and the initial timing parameters of polarity reversal, wherein the initial timing parameters include the duration of positive electrode action and the duration of negative electrode action, and assessing the degree of balance between inhibition and activation effects within a complete cycle through a physiological stress balance index; S2. Based on the preset combination of basic parameters, initialize and apply an initial superimposed electric field with the first DC bias polarity within the preservation space; S3. During the application of the superimposed electric field, monitor in real time the concentration of characteristic volatile gases released by the target fruits and vegetables in the preservation space; S4. Based on the characteristic volatile gas concentration data obtained from monitoring, generate the polarity switching decision command for the current moment; S5. In response to the switching decision command, perform the polarity switching operation of the superimposed electric field, and apply the superimposed electric field with the second DC bias polarity after the switching. S6. Repeat steps S3 to S5 to form a dynamic polarity reversal cycle based on physiological state feedback until the preservation process ends.

[0007] As a preferred embodiment of the DC and AC electric field superposition preservation method of the present invention, the preset basic parameter combination includes the peak-to-peak value of the AC voltage, the AC frequency, and the polarity switching buffer time. The physiological stress balance index is used as the optimization target, and the positive electrode effect duration and negative electrode effect duration are obtained based on the balance between the inhibition effect and the activation effect.

[0008] In a preferred embodiment of the DC and AC electric field superposition preservation method of the present invention, the characteristic volatile gas is ethylene gas, and the real-time monitoring is performed using an electrochemical ethylene gas sensor.

[0009] As a preferred embodiment of the DC and AC electric field superposition preservation method of the present invention, the method includes: acquiring several instantaneous values ​​of ethylene gas concentration based on a preset sampling period; smoothing the instantaneous values ​​of ethylene gas concentration to generate a representative value of ethylene gas concentration for the current sampling period; comparing the representative value of ethylene gas concentration for the current sampling period with a preset concentration threshold range; and generating a polarity switching decision instruction based on the comparison result.

[0010] As a preferred embodiment of the DC and AC electric field superposition preservation method of the present invention, the decision command is as follows: when the representative value of ethylene gas concentration is higher than the upper limit of the concentration threshold range, a command to switch to the positive polarity field is generated; when the representative value of ethylene gas concentration is lower than the lower limit of the concentration threshold range, a command to switch to the negative polarity field is generated; when the representative value of ethylene gas concentration is within the concentration threshold range, a command to maintain the current polarity field is generated.

[0011] As a preferred embodiment of the DC and AC electric field superposition preservation method of the present invention, the polarity switching operation is as follows: the field strength of the current superposition electric field is reduced to zero, and then the polarity of the DC bias voltage is switched from the current polarity to the opposite polarity, and a superposition electric field with the opposite polarity is reapplied.

[0012] As a preferred embodiment of the method for preserving food by superimposing DC and alternating electric fields according to the present invention, the applied first DC bias voltage is positive.

[0013] As a preferred embodiment of the DC and AC electric field superposition preservation method of the present invention, the weighted moving average method is used to smooth several instantaneous values ​​of ethylene gas concentration to generate a representative value of ethylene gas concentration.

[0014] In a second aspect, the present invention provides a computer device, including a memory and a processor, wherein the memory stores a computer program, wherein when the computer program is executed by the processor, it implements any step of the DC and AC electric field superposition preservation method as described in the first aspect of the present invention.

[0015] Thirdly, the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein: when the computer program is executed by a processor, it implements any step of the DC and AC electric field superposition preservation method as described in the first aspect of the present invention.

[0016] The beneficial effects of this invention are as follows: By maintaining a dynamic balance between the two contradictory processes of inhibiting spoilage and maintaining the body's resistance, a physiological stress balance index is set to assess the balance between inhibition and activation effects within a complete cycle. The inhibition effect of the positive electric field and the activation effect of the negative electric field over time are processed to generate initial time-series parameters in which the inhibition and activation effects can reach a dynamic balance within a complete polarity cycle. Fruits and vegetables can effectively delay spoilage and maintain sufficient vitality to resist environmental stress, thereby achieving a good preservation effect. At the same time, the real-time collected physiological signals are compared with preset thresholds, and a decision on polarity switching or maintenance is output after logical judgment, so that the preservation strategy has adaptive optimization capabilities and can make precise responses to the actual state of fruits and vegetables. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart of a method for preserving food by superimposing DC and AC electric fields.

[0019] Figure 2 This is a schematic diagram of the polarity switching decision instruction flow. Detailed Implementation

[0020] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0021] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0022] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0023] Reference Figures 1-2 As one embodiment of the present invention, this embodiment provides a method for preserving food by superimposing DC and alternating electric fields, comprising: S1. For fruits and vegetables, a basic combination of superimposed electric field parameters and initial timing parameters for polarity reversal are preset. The initial timing parameters include the duration of positive electrode action and the duration of negative electrode action. The balance between inhibition and activation effects within a complete cycle is evaluated by the physiological stress balance index.

[0024] For the target fruit and vegetable category, the operator presets a set of fixed operating parameters through the human-machine interface, including the basic parameters of the superimposed electric field, such as setting the peak-to-peak value of the alternating voltage to 12 kV and the alternating frequency to 800 Hz, as well as the initial timing parameters for polarity reversal, such as setting the initial positive polarity duration to 3 hours, the initial negative polarity duration to 1 hour, and the polarity switching buffer time to 20 seconds.

[0025] The core flaw of traditional electric field preservation technology is its reliance on experience and lack of quantitative physiological basis for setting the polarity timing. Existing technologies typically determine the duration of positive and negative polarity effects through trial and error. This method cannot guarantee finding the optimal solution, nor can it adapt to individual differences in fruits and vegetables from different batches or at different initial stages of maturity. To obtain the optimal timing setting, a physiological stress balance index is established. The initial duration of positive and negative polarity effects is set based on the physiological stress balance index, specifically as follows:

[0026] Among them, PSBI is the Physiological Stress Balance Index, used to assess the balance between inhibitory and activating effects within a complete cycle; T+ represents the duration of positive polarity effect, and T- represents the duration of negative polarity effect. Let be the intensity of the inhibitory effect of the positive polar electric field on putrefaction-related enzymes at time t, which is a function of time and electric field parameters, and is modeled as follows: ,in and For the corresponding fruit and vegetable categories, The strength of the negative polarity electric field at time t against the activation effect of the inversely correlated enzyme is modeled as follows: ,in and α is the corresponding activation coefficient, α is the activation effect weight adjustment factor used to adjust the relative importance of the activation effect in the equilibrium, and β is the smoothing constant to prevent the denominator from being zero and to increase the stability of the model.

[0027] Fruit and vegetable preservation involves a dynamic balance between two contradictory processes: inhibiting spoilage and maintaining the plant's resilience. The numerator term integrates the temporal inhibitory effect of the positive electric field, representing the total inhibitory effect. The denominator term integrates the temporal activation effect of the negative electric field, representing the total maintenance or enhancement effect. A smoothing constant is used to prevent the denominator from being zero and to enhance the model's robustness. A PSBI value approaching 1 represents the theoretical ideal state, indicating that within a complete polarity cycle, the inhibitory and activation effects reach a dynamic balance. In this state, fruits and vegetables can effectively delay spoilage while maintaining sufficient vitality to resist environmental stress, thus achieving optimal preservation. This avoids the poor preservation effect caused by the reliance on experience in setting the polarity timing in traditional electric field preservation technologies.

[0028] The range of PSBI is (0, +∞). A physiological stress balance index close to 1 indicates that the inhibitory effect and the activating effect reach an ideal balance within a cycle, at which point the preservation effect is optimal. PSBI > 1 indicates that the inhibitory effect is dominant and is suitable for fruits and vegetables with a fast spoilage process or in the early stage of storage. PSBI < 1 indicates that the activating effect is dominant and is suitable for fruits and vegetables that need to maintain strong vitality to resist aging.

[0029] For example, for Fuji apples, the initial storage period aims to inhibit browning, with a target PSBI slightly greater than 1, set at 1.2, obtained through data fitting. and After determining the specific parameters, a set of solutions for T+ and T- that make PSBI=1.2 is obtained. From these solutions, a set of solutions that conform to the actual operating cycle is selected, for example, T+ = 4 hours and T- = 1 hour, that is, the positive electrode action time is set to 4 hours and the negative electrode action time is set to 1 hour.

[0030] S2. Based on the preset combination of basic parameters, initialize and apply an initial superimposed electric field with the first DC bias polarity within the preservation space.

[0031] Based on the preset basic parameters, the drive electric field generator is started. The device first outputs a positive 10 kV DC bias voltage, and then superimposes an alternating voltage with a peak value of 12 kV and a frequency of 800 Hz to establish a stable positive polarity superimposed electric field in the preservation space.

[0032] S3. During the application of the superimposed electric field, the concentration of characteristic volatile gases released by the target fruits and vegetables in the preservation space is monitored in real time.

[0033] An electrochemical ethylene gas sensor installed in the preservation space begins to work, collecting and transmitting the ethylene gas concentration value in the space in real time at a frequency of once per minute. The ethylene concentration is used to reflect the respiration intensity and maturity of fruits and vegetables.

[0034] S4. Based on the characteristic volatile gas concentration data obtained from monitoring, generate the polarity switching decision command for the current moment.

[0035] Every minute, a weighted moving average is calculated from the latest collected ethylene concentration values ​​to generate a smoothed representative value of the current ethylene concentration. This representative value is then compared with a preset threshold range, which is set based on historical operating conditions, such as a lower limit of 0.5 ppm and an upper limit of 1.5 ppm. If the representative value exceeds the upper limit, an instruction to immediately switch to the positive polarity field is generated; if the representative value is below the lower limit, an instruction to immediately switch to the negative polarity field is generated; and if the representative value is within the range, an instruction to maintain the current polarity is generated.

[0036] S5. In response to the switching decision command, perform the polarity switching operation of the superimposed electric field, and apply the superimposed electric field with the second DC bias polarity after the switching.

[0037] If a switching command is received, the electric field strength is first reduced to zero within a 20-second buffer period, then the DC bias polarity is switched, and finally a superimposed electric field with the new polarity is reapplied. If the command is to maintain, the current polarity electric field is continued to be applied.

[0038] S6. Repeat steps S3 to S5 to form a dynamic polarity reversal cycle based on physiological state feedback until the preservation process ends.

[0039] Repeat steps S3 to S5 to form a closed-loop control loop that dynamically adjusts the polarity of the electric field based on the real-time physiological state of fruits and vegetables until the preservation process ends. Feedback adjustment enables adaptive optimization of the preservation strategy.

[0040] The preset basic parameter combination includes alternating voltage peak-to-peak value, alternating frequency, and polarity switching buffer time. The physiological stress balance index is used as the optimization target. The duration of positive and negative electrode action is obtained based on the balance between the inhibitory and activating effects.

[0041] The peak-to-peak value of the alternating voltage in the basic parameters is an important parameter of the superimposed electric field strength. It is determined according to the size of the preservation space and the characteristics of fruits and vegetables. The alternating frequency affects the effect of the electric field on microorganisms and enzymes. It needs to be selected according to the inactivation frequency range of the target harmful microorganisms. The polarity switching buffer time is used to protect the power electronic components from impact. The initial positive polarity action duration and the initial negative polarity action duration constitute the initial polarity reversal cycle, which is preset according to the main spoilage mechanism and stress resistance requirements of the target fruits and vegetables.

[0042] The characteristic volatile gas is ethylene gas, and the real-time monitoring is performed using an electrochemical ethylene gas sensor.

[0043] Ethylene is a key plant hormone in the ripening and senescence process of fruits and vegetables. Its concentration changes directly reflect the intensity of physiological activities of fruits and vegetables. An electrochemical ethylene gas sensor is used because the sensor has high sensitivity, fast response characteristics and good stability to low concentrations of ethylene, which can meet the accuracy and reliability requirements of real-time monitoring.

[0044] Based on a preset sampling period, several instantaneous values ​​of ethylene gas concentration are acquired from monitoring. The instantaneous values ​​of ethylene gas concentration are smoothed to generate a representative value of ethylene gas concentration for the current sampling period. The representative value of ethylene gas concentration for the current sampling period is compared with a preset concentration threshold range. Based on the comparison result, a polarity switching decision instruction is generated.

[0045] Using a fixed sampling period, such as 5 minutes, a set of instantaneous values ​​is extracted from continuous monitoring data. This set of data is processed using a weighted moving average method, assigning higher weights to recent data to generate a more representative concentration value that better reflects the trend and eliminates random fluctuations. The smoothed representative concentration value is compared with a preset static threshold range, and instructions are output based on the comparison results. This ensures that decisions are based on stable and reliable data and that the response strategy is clear.

[0046] The decision instructions are as follows: when the representative value of ethylene gas concentration is higher than the upper limit of the concentration threshold range, an instruction to switch to the positive polarity field is generated; when the representative value of ethylene gas concentration is lower than the lower limit of the concentration threshold range, an instruction to switch to the negative polarity field is generated; when the representative value of ethylene gas concentration is within the concentration threshold range, an instruction to maintain the current polarity field is generated.

[0047] The polarity switching operation is as follows: reduce the field strength of the current superimposed electric field to zero, then switch the polarity of the DC bias voltage from the current polarity to the opposite polarity, and reapply the superimposed electric field with the opposite polarity.

[0048] First, the electric field strength is reduced to zero to achieve electrical isolation, avoiding arcing and current surges that may occur during live switching and protecting the high-voltage power supply module. Then, the DC bias polarity is physically switched, from positive to negative or vice versa. Finally, an alternating voltage is reapplied to establish a superimposed electric field of the new polarity. This ensures equipment safety and waveform quality during the switching process.

[0049] The first DC bias applied is positive. For fruits and vegetables, the main challenge in the early post-harvest period is to suppress excessive respiration and the activity of spoilage microorganisms. A positive electric field has a significant inhibitory effect on enzymes such as polyphenol oxidase and peroxidase that cause browning and aging. Therefore, applying a positive field from the beginning is beneficial for quickly suppressing the physiological activity of fruits and vegetables in the early stages of preservation, creating favorable conditions for long-term storage.

[0050] Directly using a single instantaneous concentration value for decision-making is highly susceptible to misjudgment due to sensor errors or minor environmental disturbances, leading to unnecessary polarity switching and disrupting the stability of the preservation environment. The weighted moving average method, by smoothing multiple data points within a time window, effectively filters out high-frequency random noise and extracts low-frequency signals that reflect the true trend of concentration changes. The weighted moving average method was used to smooth several instantaneous ethylene gas concentration values ​​to generate a representative ethylene gas concentration value. When used to process time series data, the weighted moving average method assigns different weights to data at different time points, highlighting the importance of recent data and thus more accurately capturing data trends.

[0051] The expression for the representative value of ethylene gas concentration is:

[0052] in, This represents the concentration of ethylene gas produced. Let i be the instantaneous value of the ethylene gas concentration. The weighting coefficient corresponding to the i-th concentration value is assigned in a linear decreasing manner. For example, the weight of the latest data is n, the weight of the previous data is n-1, and so on. n is the number of sampling points in a sampling period. By weighting the data, signal noise is effectively suppressed, stable input is provided, and the basic function of feedback control is realized.

[0053] This embodiment also provides a computer device applicable to the preservation method of superimposed DC and alternating electric fields, including: a memory and a processor; the memory is used to store computer-executable instructions, and the processor is used to execute the computer-executable instructions to realize the preservation method of superimposed DC and alternating electric fields as proposed in the above embodiment.

[0054] The computer device can be a terminal, comprising a processor, memory, communication interface, display screen, and input devices connected via a system bus. The processor provides computing and control capabilities. The memory includes non-volatile storage media and internal memory. The non-volatile storage media stores the operating system and computer programs. The internal memory provides an environment for the operation of the operating system and computer programs stored in the non-volatile storage media. The communication interface is used for wired or wireless communication with external terminals; wireless communication can be achieved through Wi-Fi, carrier networks, NFC (Near Field Communication), or other technologies. The display screen can be an LCD screen or an e-ink screen. The input devices can be a touch layer covering the display screen, buttons, a trackball, or a touchpad on the computer device's casing, or an external keyboard, touchpad, or mouse.

[0055] This embodiment also provides a storage medium storing a computer program, which, when executed by a processor, implements the method for preserving food by superimposing DC and alternating electric fields as proposed in the above embodiments. The storage medium can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as Static Random Access Memory (SRAM), Electrically Erasable Programmable Read-Only Memory (EEPROM), Erasable Programmable Read Only Memory (EPROM), Programmable Red-Only Memory (PROM), Read-Only Memory (ROM), magnetic storage, flash memory, magnetic disk, or optical disk.

[0056] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preserving food using a superposition of direct current and alternating electric fields, characterized in that: include, S1. For fruits and vegetables, a basic combination of superimposed electric field parameters and initial timing parameters for polarity reversal are preset. The initial timing parameters include the duration of positive electrode action and the duration of negative electrode action. The balance between inhibition and activation effects within a complete cycle is evaluated by the physiological stress balance index. S2. Based on the preset combination of basic parameters, initialize and apply an initial superimposed electric field with the first DC bias polarity within the preservation space; S3. During the application of the superimposed electric field, monitor in real time the concentration of characteristic volatile gases released by the target fruits and vegetables in the preservation space; S4. Based on the characteristic volatile gas concentration data obtained from monitoring, generate the polarity switching decision command for the current moment; S5. In response to the switching decision command, perform the polarity switching operation of the superimposed electric field, and apply the superimposed electric field with the second DC bias polarity after the switching. S6. Repeat steps S3 to S5 to form a dynamic polarity reversal cycle based on physiological state feedback until the preservation process ends.

2. The method for preserving food by superimposing DC and AC electric fields as described in claim 1, characterized in that: The preset basic parameter combination includes alternating voltage peak-to-peak value, alternating frequency, and polarity switching buffer time. The physiological stress balance index is used as the optimization target. The duration of positive and negative electrode action is obtained based on the balance between the inhibitory and activating effects.

3. The method for preserving food by superimposing DC and AC electric fields as described in claim 2, characterized in that: The characteristic volatile gas is ethylene gas, and the real-time monitoring is performed using an electrochemical ethylene gas sensor.

4. The method for preserving food by superimposing DC and AC electric fields as described in claim 3, characterized in that: Based on a preset sampling period, several instantaneous values ​​of ethylene gas concentration are acquired from monitoring. The instantaneous values ​​of ethylene gas concentration are smoothed to generate a representative value of ethylene gas concentration for the current sampling period. The representative value of ethylene gas concentration for the current sampling period is compared with a preset concentration threshold range. Based on the comparison result, a polarity switching decision instruction is generated.

5. The method for preserving food by superimposing DC and AC electric fields as described in claim 4, characterized in that: The decision instructions are as follows: when the representative value of ethylene gas concentration is higher than the upper limit of the concentration threshold range, an instruction to switch to the positive polarity field is generated; when the representative value of ethylene gas concentration is lower than the lower limit of the concentration threshold range, an instruction to switch to the negative polarity field is generated; when the representative value of ethylene gas concentration is within the concentration threshold range, an instruction to maintain the current polarity field is generated.

6. The method for preserving food by superimposing DC and AC electric fields as described in claim 5, characterized in that: The polarity switching operation is as follows: reduce the field strength of the current superimposed electric field to zero, then switch the polarity of the DC bias voltage from the current polarity to the opposite polarity, and reapply the superimposed electric field with the opposite polarity.

7. The method for preserving food by superimposing DC and AC electric fields as described in claim 1, characterized in that: The first DC bias voltage applied is positive.

8. The method for preserving food by superimposing DC and AC electric fields as described in claim 5, characterized in that, The weighted moving average method was used to smooth several instantaneous values ​​of ethylene gas concentration to generate representative values ​​of ethylene gas concentration.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that: When the processor executes the computer program, it implements the steps of the method for preserving food by superposition of DC and AC electric fields as described in any one of claims 1 to 8.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by the processor, it implements the steps of the method for preserving food by superposition of DC and AC electric fields as described in any one of claims 1 to 8.

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