DC1
Dual Core 1, or DC1, is a schedule which logically follows Segmented sleep, and it is the first Dual Core schedule, with the reduction of some sleep from the second core of Segmented and the addition of one daytime nap to compensate for the reduced amount of REM in the second core. This allows for some sleep reduction on the schedule, and polyphasic sleepers will now officially be able to learn to nap, as Segmented sleep does not have any naps.
DC1 is also considered an ideal polyphasic schedule to attempt, given his total sleep, which ranges from ~5.3-6.3h and is very friendly for beginners.
Mechanism
DC1's mechanisms largely carry on from the original Segmented sleep. Each core sleep is located around each respective sleep peak to further consolidate the overall sleep structure. The first core may remain around the same length or some slight reduction compared to the first core of Segmented sleep, to preserve the amount of SWS, while the second core is reduced in length so that REM can be alleviated in the nap. The nap also serves to bridge the long daytime wake gap which has increased because of the reduced total sleep from both cores combined. However, the nap on DC1 does not always guarantee a high percentage of REM sleep. For some attempters, it only contains NREM2, or very small amount of REM, especially if the nap is placed somewhat late in the afternoon (after ~3 PM). Despite all that, the nap can sustain alertness for a long time until the first core (~7-8h) , because it is generally easier to stay awake in the day than during the night (~4-5h between 2 cores).
DC1 is often compared to E2, because both of them are the first schedules in their respective schedule series (Dual Core & Everyman). They have a similar amount of total sleep and the same number of sleep blocks (3) per day. The only difference is that E2's first nap is now a core in DC1, and that DC1's first core is recommended to start earlier than E2 core.
Adaptation
There are 2 methods to adapt to DC1. The mainstream method is often cold turkey, a straight transition from monophasic sleep. Another method is to first adapt to Segmented sleep and then transition to DC1. Each method has pros and cons.
Cold turkey
This method mostly benefits naturally Segmented sleepers, who are accustomed to waking up at night or even involuntarily doing Segmented sleep without their own awareness. Non-natural Segmented sleepers can also jump into DC1 cold turkey if there is not enough time to pull off a gradual adaptation, but the adaptation process is considered much more strenuous, except the extended variants. Regardless of the disadvantage, several cold turkey adaptations to DC1 and its extended versions have reported success.
Gradual adaptation
This adaptation is likely slower than cold turkey, but the transition is designed to be less stressful from an adapted Segmented to a new DC1. However, there is no guaranteed success for DC1, and this method actually has seen lower success rate than the cold turkey method. This is largely due to the amount of time it would take to achieve good results on 2 successive adaptations.
However, for sleepers who have been adapted to Segmented and remain on it for a long time, the transition to DC1 at this point puts them on equal grounds with natural Segmented sleepers who are about to start a DC1 adaptation.
Alternate variations
Extended sleep cycles
This option is considered standard. It usually has 3h20m first core and 1h40m second core, theoretically making sleep cycles a bit longer (close to 100m). In fact, according to EEG readings of some community members, sometimes cycle lenght might be unchanged and shorter, so there is more LNREM inserted in the end of cores.[1][2]
Standard sleep cycles
This variation is rarely used and has a lower success rate since cores contain less light sleep/REM. It is considered more difficult than the standard one, and usually fits people with lower natural monophasic sleep baseline, about 6-7 hours or less.
Equal core length
Both cores are of the same length. This variation is viable, but rare. It is also considered more difficult than the standard one, since requires sleep cycle compression.
Swapped cores
In this variation the first core is swapped with the second one. The difficulty is also higher, because of the possible SWS wakes and the need for SWS splitting, which is easier for either experienced polyphasic sleepers or those with lower SWS sleep requirements.
Extended
The easiest and a popular option, which has several variations. Usually 3h+3h or 4.5h+1.5h core versions are used, but other options are also possible (e.g. 1.5h+4.5h or 3.5h+3.5h). It usually has 4 cycles instead of 3 (5 or more is also possible, but almost never is used). This variation fits adolescents or those with higher sleep requirements.
Shortened
This option has only 2 sleep cycles, for example 1.5h+1.5h or 2h+2h. Is much harder and recommended only for those with lower sleep needs, 6h mono or less. It allows for much less LNREM/REM.
