JP2006085879A - Optical information recording medium and method for setting optimum recording power of the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optimum recording power setting method which enhances the precision in an optimum recording power setup and is effective in a phase-change optical information recording medium recordable at high speed, in the case of erasing a mark in a test recording area, by forming a more stable state of the test area, and an optical information recording medium preformatted with the setting method. <P>SOLUTION: (1) In this optimum recording power setting method of the optical information recording medium, test recording is performed by sequentially varying recording power to the test recording area predefined on the optical information recording medium, and the recorded test area is reproduced. In evaluating a reproducing signal, and before a test recording operation, all or some of the test recording area is irradiated and scanned with pulsed intensity-modulated light. (2) In the optimum recording power setting method of the optical information recording medium described in (1), the pulsed intensity-modulated light includes a portion which is alternately irradiated with two kind of pulses which are constituted of pulses of power P1 and pulse width T1 and pulses of power P2 and pulse width T2, and satisfies P1>P2 and T1≤T2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  In the present invention, recording / reproducing / erasing / rewriting is possible by intensity modulation of light irradiated with a phase change material as a recording material, as typified by DVD-RAM, DVD-RW, DVD + RW, and CD-RW. The present invention relates to a phase change type optical information recording medium, and more particularly to a phase change type optical information recording medium capable of recording at high speed represented by DVD + RW and CD-RW, and an optimum recording power setting method thereof.

In recent years, the capacity of digital information has been increasing. In order to store a large amount of digital information (for example, voice / image), an information recording medium having a high transfer rate is required. In particular, phase-change optical information recording media have attracted attention because they can be rewritten, have portability, and can be reproduced by a reproduction-only apparatus that has become widespread. In particular, CD-RW, DVD-RW, and DVD + RW are attracting attention as removable media having high playback compatibility because they can be played back by widely used DVD-ROM playback devices.
As means for improving the transfer speed of these phase change type optical information recording media, it is conceivable to increase the density and increase the scanning speed. However, increasing the density by changing the track pitch and the minimum mark size is used for reproduction. The optical system of the apparatus is changed and reproduction compatibility is lost. On the other hand, increasing the scanning speed is an effective means because the transfer speed can be improved without changing the optical system of the reproducing apparatus.

  However, in the phase change optical information recording medium, information is recorded / rewritten by irradiating the recording layer material with laser light and controlling the thermal history of the recording layer. That is, information is recorded by utilizing the dynamic thermal characteristics of the recording layer material. Specifically, recording is performed by melting and quenching to an amorphous state and heating to a temperature higher than the crystallization temperature to obtain a crystalline state. In order to cope with recording at a higher scanning speed, it is necessary to crystallize in a shorter heating time. Therefore, it is essential to select a recording layer material having a high crystallization speed. Such a material with a high crystallization rate has a major problem that it is deteriorated with time regardless of whether it is recorded or not. The mechanism of deterioration over time is not clear, but if recording (shelf test) is performed after a while in an unrecorded state, the recording sensitivity will decrease and the mark length / mark length (space) jitter will increase. This is presumed to be a phenomenon of relaxation of the crystalline state of the recording layer. That is, it is considered that the crystal state such as an unrecorded part immediately after recording or immediately after recording or between amorphous marks (spaces) is relaxed to a more stable state.

The recording apparatus performs test recording for setting optimum recording conditions before recording information on the changeable optical information recording medium. In particular, a method for setting the optimum recording power by performing test recording while sequentially changing the recording power and evaluating the reproduction signal of the test recording portion is called OPC (Optimum Power Control). In normal OPC, the procedure is as follows.
(1) Erase the marks in the test recording area provided on the medium.
(2) Test recording is performed by sequentially changing the recording power.
(3) The reproduction signal in the test recording area is evaluated and the optimum recording power is calculated.
However, in the case of a phase change type optical information recording medium that can be recorded at a higher speed, which is the subject of the present invention, it is difficult to completely erase the recording mark by this method, and at the same time, the optimum recording power can be stabilized. It is very difficult to calculate, and the reproduction signal varies greatly depending on the number of repeated recordings and the elapsed time from the last recording.

In addition, by irradiating and scanning light with no intensity modulation at an optimum erasing power Pe = ε × Pwo obtained by multiplying the optimum recording power Pwo by ε (a constant specific to a medium of less than 1), a mark that has already been recorded A technique for determining the optimum recording power by performing trial writing after erasing is also known, but it is a sufficiently satisfactory method for a phase-change optical information recording medium that can be recorded at a higher speed, which is a subject of the present invention. Absent.
In addition to the above, Patent Document 1 discloses an optical recording medium in which power information of an erase pattern is stored. Mark erase is performed by irradiating and scanning light modulated in a pulse shape. However, the pulse-like erasing pattern is for creating at the same time as the mark at the time of direct overwriting, and controls the amplitude and offset of the intensity-modulated light in a pulse shape according to recording / erasing, The object, effect, and method are different from the present invention.

JP 2003-338049 A

  The present invention provides a phase-change optical information recording medium capable of high-speed recording, which improves the accuracy of optimum recording power setting by making the state of the test area more stable when erasing marks in the test recording area. An object is to provide an effective optimum recording power setting method and an optical information recording medium preformatted with the setting method.

The above problems are solved by the following inventions 1) to 5) (hereinafter referred to as the present inventions 1 to 5).
1) Perform test recording in the specified test recording area on the optical information recording medium while sequentially changing the recording power, reproduce the test recorded area, and evaluate the reproduced signal. A method for setting an optimum recording power of an optical information recording medium, characterized by irradiating and scanning all or a part of a test recording area with light whose intensity has been modulated in a pulse form before.
2) The light intensity-modulated in a pulse form includes a portion that alternately irradiates two kinds of pulses, a pulse having a power P1 and a pulse width T1, and a power P2 having a pulse width T2, and P1> P2 And the optimum recording power setting method for an optical information recording medium according to 1), wherein T1 ≦ T2 is satisfied.
3) When the pulse scanning before test recording is performed at the scanning speed V on the optical information recording medium in which the maximum scanning speed at the time of recording is Vw and the recording channel bit at Vw is Tw, the following relational expression is obtained. 2) The optimum recording power setting method for an optical information recording medium according to 2).
T1 + T2 ≦ 2Tw
0.2Vw ≦ V ≦ 0.8Vw
4) An optical information recording medium in which information relating to the relational expression described in 3) is preformatted.
5) The light according to 4), which has at least a lower protective layer, a recording layer, an upper protective layer, and a reflective layer on a transparent substrate, and the recording layer contains Ga, Sb, Sn, and Ge as main components. Information recording medium.

Hereinafter, the present invention will be described in detail.
The application target of the optimum recording power setting method of the present invention is a phase change type optical information recording medium such as a rewritable optical disk. Specifically, they are DVD + RW, DVD-RW, CD-RW, PD (Blu-ray Disc), and the like. In these optical information recording media, the recording layer material is irradiated near the melting point by irradiating condensed light onto a crystalline recording layer laminated on a substrate (in many cases, sandwiched between inorganic protective layers). Alternatively, it is heated to a melting point or higher and melted, and then rapidly cooled by reducing the intensity of irradiated light to form an amorphous mark. On the other hand, the amorphous mark portion is irradiated with condensed light and heated to a temperature near the crystallization temperature (temperature lower than the melting point) or above the crystallization temperature and below the melting point to form a crystalline state, thereby erasing the amorphous mark.
The crystal-amorphous state change is a reversible phase change, and the phase change can be caused only by temperature modulation, that is, intensity modulation of irradiated light. Further, since the optical constants are different between the crystalline state and the amorphous state, the amorphous state and the crystalline state can be discriminated by light by using this difference in optical physical properties. Therefore, information can be recorded with amorphous marks.

As the phase change recording material, a material mainly composed of SbTe is mainly used, and GeInSbTe, AgInSbTe, GeGaSbTe, GeSbTe, and the like are widely used. In addition, examples of recording layer materials that can support recent high-speed recording (equivalent to 8 × speed for DVD and 24 × speed for CD) include GeSbSn, GeInSbSn, GeInSbSnTe, GaSbSn alloy, GaGeSbSn alloy, and GaGeSbSnTe alloy. Since these materials have a high crystallization speed, direct overwrite (DOW) is possible even at high-speed recording.
The recording layer is laminated on a transparent substrate. A guide groove (groove) may be provided on the transparent substrate for positioning (tracking) the collected light. In order to prevent diffusion and chemical reaction due to heating, protective layers may be provided above and below the recording layer.
The protective layer material is preferably a stable substance that has a higher melting point than the recording layer material and does not cause a chemical reaction, and is preferably transparent in the wavelength region of light used for recording and reproduction. Specifically, a simple substance or a mixture of metal oxide, sulfide, and nitride is preferable, and a mixture of ZnS and SiO ₂ is generally used.

Further, a reflective layer may be provided above the recording layer (on the opposite side of the substrate). When the protective layer is provided, the reflective layer is formed on the protective layer. By providing the reflective layer, the reflectance during reproduction can be kept high, so that the reliability of the reproduced signal is improved.
As the reflective layer material, any metal / alloy is used, but Al, Ag, and Au are generally used. Furthermore, you may use the alloy which added arbitrary metal elements to these metals.
If the reflective layer is not provided, or if the reflective layer is provided and the film thickness is small, a separate heat diffusion layer that efficiently releases heat generated in the vicinity of the recording layer during recording is required. When the reflective layer is sufficiently thick, the reflective layer can also serve as the heat diffusion layer.
As the thermal diffusion layer, any metal / alloy material having a high thermal conductivity can be used. In the case of a multilayer optical recording medium in which a plurality of recording layers are laminated, a high light transmittance is also required for the thermal diffusion layer. As a material for the heat diffusion layer, a material used for the transparent electrode is preferable. Specific examples include ITO, Sn oxide, zinc oxide and the like.
Furthermore, the same structure may be laminated on the reflective layer or the heat diffusion layer to form a multilayer disk. Further, a protective layer made of resin may be provided, and the substrate may be bonded with an adhesive or the like.

Information recording on the optical information recording medium is performed by a recording / reproducing apparatus as shown in FIG. Recording / reproduction is performed by condensing light with an optical pickup unit and irradiating the recording layer near the medium. The irradiated light is reflected by the medium, returns to the optical pickup unit, and is incident on the photodetector by a polarized beam splitter (PBS).
Light intensity modulation at the time of recording is performed by the strategy creation unit, and a pulse pattern is set. The irradiation power is set in the power setting unit. Each output drives a laser diode through a laser driver. Signal reproduction after recording is performed by converting the reflected light into an electrical signal by a photodetector and measuring the signal with a measurement unit.
These recording conditions and reproduction signals are associated with each other in the calculation unit, and the measured values are handled as functions with the recording conditions as parameters. It is possible to feed back optimum recording conditions by evaluating the function.

Information is recorded with the mark length and mark length modulated. Examples of mark length / inter-mark length recording include EFM (8-14 modulation) employed in compact discs, EFM + employed in DVD, and 1-8 modulation.
In the mark length / inter-mark length modulation, each time length is expressed by nT with respect to the channel bit T. Here, n is a finite natural number, but its range is determined by the modulation method. In the case of EFM +, n is set to 3 to 11 and 14.
Marks having these lengths are formed by entering and scanning light whose intensity is modulated. When the scanning speed at the time of recording is v and the channel bit at the time of recording is Tw, the density of the recording information can be kept constant by keeping v × Tw constant. Therefore, in order to record information at high speed, it is necessary to increase v and shorten Tw.
V and Tw for recording DVD + RW at the normal 8 × speed are as follows.
v = 3.49 m / s × 8 = 27.9 m / s
Tw = 4.78ns

The method of intensity modulation at the time of recording is called a recording strategy.
Since the target of the optimum recording power determination method of the present invention is a rewritable phase change type optical information recording medium, recording is performed by alternately irradiating a heating pulse of irradiation power Pw and a cooling pulse of irradiation power Pb. Erase. The relationship between the irradiation powers is Pw>Pe> Pb. Pe is the erase power. Furthermore, it is preferable that Pe <0.6Pw and Pb ≦ 1 mW. In general, the number of pulses is set to n-1 with respect to the nT mark. That is, when the mark length increases by 1T, the heating pulse and the cooling pulse are increased one by one. Therefore, the light emission period of the pulse to be irradiated is set to 1T.

However, 1Tw becomes 4.78 ns when it corresponds to the above-mentioned 8 × speed of DVD. When the lengths of the heating pulse and the cooling pulse are each set to 0.5 Tw, the pulse width is 2.39 ns. Usually, since the rise time and fall time of the laser are 1.7 ns or more, it becomes impossible to irradiate the light emission pulse of 0.5 Tw. That is, the irradiation power of a sufficiently high heating pulse cannot be reached, and at the same time, the irradiation power of a sufficiently low cooling pulse cannot be reached, and as a result, sufficient heating and cooling are not performed and mark formation becomes difficult.
As a countermeasure, the 2T strategy was adopted in US CD-RW.
An example of a 2T strategy is shown in FIG. The following relationship holds between the mark length nT and the number of heating pulses m.
n = 2m (when n is an even number)
n = 2m-1 (when n is an odd number)
Thereby, the light emission period of a pulse becomes 2T-3T. As a result, the light emission period of the pulse can be set to Tw = 9.56 to 14.34 ns, which is equivalent to 8 × speed of DVD, and the recording layer is rapidly cooled in order to allow sufficient irradiation time of the heating pulse and irradiation time of the cooling pulse. And an amorphous mark can be formed. For marks longer than 4T, the mark length can be controlled by controlling the positions of the first pulse and the last pulse. However, in the 3T mark pattern, it is necessary to form a mark with one set of heating pulse and cooling pulse.

Regardless of which strategy is used, since the recording power, that is, the irradiation power of the heating pulse, greatly affects the recording characteristics, the recording apparatus performs test recording in the test recording area provided on the medium to set the optimum recording power ( OPC mentioned above).
In order to perform OPC, it is necessary to provide a test recording area on the medium. This area needs to be set outside the information area of the medium. Therefore, in the case of a disk-shaped medium, it is preferable to provide it in the innermost or outermost region. Examples of test recording areas include CD-RW PCA (Power Calibration Area), DVD + RW Inner Drive Test Zone (inner drive test zone), Outer Drive Test Zone (outer drive test zone), and the like. It is done.

The recording apparatus performs test recording in these areas, but erases marks existing in the test recording area and makes the reflectance and physical properties of the medium uniform before the test recording. Usually, this operation before test recording is performed by irradiating and scanning DC light (light without intensity modulation) on the test recording area of the medium. This operation makes the test recording area more stable, so it is possible to improve the reproducibility when performing test recording under the same conditions, and to minimize the change in the optimum recording power due to the number of DOWs. It becomes.
However, it has been clarified that in the optical information recording medium corresponding to the high-speed and high-density recording of DVD + RW of 8 times or more, the test recording area is not sufficiently uniform by the conventional DC light irradiation / scanning.
In an optical information recording medium compatible with high-speed and high-density recording, there is a tendency that the crystalline state changes with time as the crystallization speed increases. As a result, when recording is performed while sequentially changing the recording power, the optimum recording power varies depending on the number of recordings in the test recording area and the elapsed time from the last recording. Media recorded with different recording powers are not preferable because the repeated recording durability and the reliability of the reproduced signal are significantly reduced.

In the optimum recording power setting method of the present invention, the test recording area of the medium is made uniform by irradiating and scanning the intensity-modulated light instead of the conventional method of irradiating and scanning with DC light.
Intensity modulation is performed by scanning at a speed V while alternately irradiating a pulse of irradiation time T1 with power P1 and a pulse of irradiation time T2 with power P2. Here, it is preferable that P1> P2 and T1 ≦ T2.
These irradiation / scanning conditions differ depending on the maximum recording scanning speed Vw corresponding to the medium and the recording channel bit Tw at Vw. V needs to be lower than Vw, and a range of 0.2 Vw ≦ V ≦ 0.8 Vw is preferable. The power P1 is preferably set in the vicinity of the optimum recording power at the maximum recording speed, and P2 is preferably set in the vicinity of the above-described cooling pulse irradiation power. Moreover, it is preferable that T1 + T2 ≦ 2Tw.
If the test recording area is made uniform under the above conditions, the recording layer is irradiated with scanning at a low frequency with a high-frequency pulse, and the test recording area is considered to be melt crystallized. This state is considered to be close to the crystalline state after repeated recording. On the other hand, conventional DC light irradiation / scanning is considered to be solid phase initialization, which differs from the crystalline state after repeated recording.
Therefore, by irradiating and scanning the intensity-modulated light, a uniform test recording area close to repeated recording can be obtained.

Test recording is performed by sequentially changing the recording power in the uniform test recording area. The method for sequentially changing the recording power can be arbitrarily set. Although it may be changed continuously, it is preferably changed stepwise. In this case, the recording condition and the address of the test recording area must be associated with each other.
The optimum recording power is calculated by reproducing and evaluating the test recording area. Any characteristic can be used as a characteristic to be evaluated during reproduction, but a parameter related to signal amplitude is preferable because it has high sensitivity to recording sensitivity. Examples of such parameters include the degree of modulation and asymmetry. These parameters are processed as a function of recording power.
An existing method can be used as a method for calculating the optimum recording power. For example, the γ method using the degree of modulation, the β method using asymmetry, and the like can be mentioned. For the phase change optical information recording medium, the γ method is common and preferable.
For the calculation, processing on a computer such as smoothing of a parameter by an approximate expression may be performed.
P1, P2, T1, T2, and V, which are parameters for recording conditions, OPC, and the above-described equalization parameters, are unique to the medium. Therefore, the information may be preformatted on the medium, or information that can uniquely calculate the information. An existing method can be used as a parameter pre-formatting method. Examples include AT-IP Extra Information (ATIP extra information) of CD-RW and Physical Information (physical information) of DVD + RW.

According to the first to third aspects of the present invention, by making the test recording area in a stable state that does not depend on the number of DOWs before the test recording, the reproducibility of the reproduction signal with respect to the recording condition (power) in the test recording becomes high. Therefore, it is possible to set the optimum recording power with higher accuracy.
According to the fourth to fifth aspects of the present invention, the optimum recording conditions for the medium are preformatted, and furthermore, a phase change material that can be recorded at a scanning speed of 20 m / s or more is used as the recording layer material. A highly reliable optical information recording medium can be provided.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited by these Examples.

Example 1
On the transparent substrate for DVD + RW, a lower protective layer, a recording layer, an upper protective layer, a corrosion prevention layer, and a reflective layer were sequentially laminated by sputtering. A mixture of ZnS and SiO ₂ generally used for phase change optical disks was used as the protective layer material, and a GaSbSnGe alloy was used as the recording layer. Since Ag was used for the reflective layer, an SiC corrosion prevention layer was provided in order to prevent reaction with the adjacent upper protective layer. Further, a transparent substrate was bonded to the upper side of the reflective layer through an adhesive material to obtain a disk having a thickness of 1.2 mm. This disk was entirely initialized (the recording layer was crystallized) to produce a DVD + RW disk. The completed DVD + RW disc has a reflectivity of about 20% and can be recorded at a speed equivalent to 8 × DVD.
Recording was performed while the recording power was sequentially changed in the outer drive test zone, which is a test recording area on the outer periphery of the DVD + RW disc, and the degree of modulation was measured.
For recording / reproduction, DDU1000 (λ = 659 nm of optical pickup, NA = 0.65 of an optical pickup) manufactured by Pulstec Industrial Co., Ltd., which is a DVD + RW disk evaluation apparatus, was used.
The conditions for making the test recording area uniform were as follows.
P1 = 30mW
P2 = 0.1mW
T1 = 3.0ns
T2 = 6.5 ns
V = 14.0 m / s
As a result of observing the RF reproduction signal after homogenization, it was confirmed that the irradiated portion was in a crystalline state and the reflectance was uniform.
Test recording was performed by sequentially changing the recording power in the uniform area. As the data to be recorded, a random pattern modulated in EFM + was recorded. As the recording strategy, a 2T strategy as shown in FIG. 2 was used. The recording speed was equivalent to 8 times the speed of DVD + RW. That is, Tw = 4.8 ns and Vw = 27.9 m / s. The test recording area was reproduced and the modulation degree was measured. The degree of modulation was measured as a function of recording power. The results are shown in FIG.
Further, the test recording area was overwritten with a recording power of 32 mW, and the degree of modulation was measured after the test recording area was similarly made uniform. This operation was repeated 10 times. The results are shown in FIG.
As can be seen from FIG. 3, the recording power dependency of the modulation degree is almost the same regardless of the number of repeated recordings. The optimum recording power setting for DVD + RW is the γ method for calculating the optimum recording power from the relationship between the modulation factor and the power. Therefore, it has been found that by using the method of the present invention, the optimum recording power can be calculated regardless of the number of repeated recordings.

Comparative Example 1
For the DVD + RW disc created in Example 1, DC light with a power of 7.4 mW was used and the test recording area was made uniform at a scanning speed of 28.9 m / s. The power is the optimum erasing power, and the scanning speed is equivalent to eight times the speed of DVD + RW which is the maximum recording speed of the medium.
Using the same recording strategy as in Example 1, the recording power was successively changed in the uniformed area to perform test recording, and the modulation degree was measured in the same manner. The result is shown in FIG.
From FIG. 4, it can be seen that the power dependency of the degree of modulation varies greatly depending on the number of repeated recordings. Therefore, the recording power cannot be calculated stably when the γ method is used.

Example 2
Using the DVD + RW disc created in Example 1, the difference ΔM [ΔM = ΔM] between the first modulation degree (M1) and the modulation degree (M10) after 10 repetitions at a recording power of 28 mW in the same manner as in Example 1. (M10-M1) / M10] was measured.
The relationship between ΔM and scanning speed V is shown in FIG. However, the horizontal axis is the amount normalized at the corresponding maximum recording scanning speed Vw = 27.9 m / s of the disk.
As can be seen from FIG. 5, ΔM was 0.01 or less when V / Vw was in the range of 0.2 to 0.8. In the region where V / Vw exceeds 0.8, the reflectance after the homogenization treatment tends to be remarkably lowered. That is, it is thought that it has become amorphous. For this reason, in the region where the recording power is low, the reflectance cannot be sufficiently returned, and the error of the modulation degree tends to increase.

Example 3
Except that the recording power was changed to 34 mW, the scanning speed was fixed to 14.0 m / s, and T1 + T2 = 2Tw = 9.6 ns, and T1 and T2 were varied, the same as in Example 2. ΔM was measured.
FIG. 6 shows the measurement result of the ΔM dependency on T1 / (T1 + T2), which is the ratio of T1 and T2.
As can be seen from FIG. 6, by setting T1 / (T1 + T2) ≦ 0.5, that is, T1 ≦ T2, ΔM is reduced, and a stable modulation degree can be obtained regardless of the number of repetitions. Therefore, it is possible to improve the accuracy when the OPC method using the modulation degree is used.

The figure which shows an example of a recording / reproducing apparatus. The figure which shows the example of 2T strategy. FIG. 6 is a diagram illustrating a measurement result of a modulation degree according to the first embodiment. The figure which shows the measurement result of the modulation degree of the comparative example 1. The figure which shows the relationship between V / Vw of Example 2, and (DELTA) M. The figure which shows the relationship between T1 / (T1 + T2) of Example 3, and (DELTA) M.

Claims (5)

  When performing test recording in a specified test recording area on the optical information recording medium while sequentially changing the recording power, reproducing the test recorded area, and evaluating the reproduced signal, before the test recording operation, A method for setting an optimum recording power of an optical information recording medium, characterized by irradiating and scanning all or a part of a test recording region with light whose intensity is modulated in a pulse form.   The light intensity-modulated in a pulse shape includes a portion that alternately irradiates two kinds of pulses, that is, a pulse having a pulse width T1 at power P1 and a pulse having a pulse width T2 at power P2, and P1> P2 and 2. The optimum recording power setting method for an optical information recording medium according to claim 1, wherein T1 ≦ T2 is satisfied. The following relational expression should be satisfied when pulse irradiation before test recording is performed at a scanning speed V on an optical information recording medium in which the maximum scanning speed during recording is Vw and the recording channel bit at Vw is Tw. The method for setting the optimum recording power of the optical information recording medium according to claim 2.
T1 + T2 ≦ 2Tw
0.2Vw ≦ V ≦ 0.8Vw   4. An optical information recording medium, wherein information relating to the relational expression according to claim 3 is preformatted. 5. The optical information according to claim 4, wherein at least a lower protective layer, a recording layer, an upper protective layer, and a reflective layer are provided on a transparent substrate, and the recording layer is mainly composed of Ga, Sb, Sn, and Ge. recoding media.

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