Here is the design of a clinical trial:

Official Title: The Impact of Concurrent Brain Stimulation and Working Memory Training on Cognitive Performance in Acquired Brain Injury

Included conditions:
- Acquired Brain Injury

Study Armgroups:
- {'label': 'Active tDCS', 'type': 'EXPERIMENTAL', 'description': 'During cognitive training in the first 2 weeks, participants will also received brain stimulation. The investigators will use a total current intensity of 2mA for 20 minutes, preceded by 30 seconds ramping up and followed by 30 seconds ramping down (total stimulation time = 21s).', 'interventionNames': ['Device: Active tDCS']}
- {'label': 'SHAM tDCS', 'type': 'SHAM_COMPARATOR', 'description': 'During sham stimulation, concurrent with the cognitive training, The investigators will use the same setup as in the active condition but after ramping up, the current will be brought back to zero and the process repeated 30 seconds before the end of the 21 minutes time interval (total sham stimulation time = 21s).', 'interventionNames': ['Device: SHAM tDCS']}

Interventions:
- {'type': 'DEVICE', 'name': 'Active tDCS', 'description': 'For the first two weeks of the study, participants will receive 20 min of brain stimulation, concurrent with cognitive training. Electrodes will be placed over the dorsolateral prefrontal cortex (active electrode), and the contralateral supraorbital site (return electrode).', 'armGroupLabels': ['Active tDCS']}
- {'type': 'DEVICE', 'name': 'SHAM tDCS', 'description': 'For the first two weeks of the study, participants will receive 20 min of SHAM brain stimulation, concurrent with cognitive training. Electrodes will be placed over the dorsolateral prefrontal cortex (active electrode), and the contralateral supraorbital site (return electrode).', 'armGroupLabels': ['SHAM tDCS']}

Primary Outcomes:
- {'measure': 'Changes in memory capacity, as measured by number of items that are memorised successfully, in the cognitive task used as the training regime;', 'description': 'The difficulty of the training regime is manipulated by increasing N, i.e. the number of items the participant is requested to memorise. As such, N is used to measure individual memory capacity. Changes in memory capacity, as the training regime progresses is the primary outcome measure of this study.', 'timeFrame': 'On day1, at end of week 2, at end of week 5 and at end of week 9'}

Please estimate the sample size based on the assumption: 
The significance level (alpha) is set at 0.05, and the power is set at 0.80. A post hoc power analysis will be conducted to assess the appropriateness of the sample size for detecting differences in a clinical population.
Sample size calculation
        The chosen sample size is based partly on the available literature that examines the effects of cognitive training on healthy young and older volunteers and additional pilot data collected in our laboratory from healthy young and elderly adults. Specifically, a statistical power analysis was performed for sample size estimation, based on data from Au et al. [39], comparing the ACTIVE (right-tDCS, 20 subjects) to the CONTROL (SHAM, 22 subjects) group. The effect size (ES) in this study was 0.73, considered to be medium to large using Cohenâs criteria [55]. With an alphaâ=â.05 and powerâ=â0.80, the projected sample size needed with this effect size (GPower 3.1) is approximately Nâ=â48 for this simplest between group comparison.
        Evidence has shown that individuals with low initial performance respond better to brain stimulation [56]. As we expect ABI patients in our sample to have low baseline performance, due to our selection criteria, we may also expect them to respond better to the intervention, therefore showing larger effects. Assuming, as explained above, that larger effects could reasonably be expected in a clinical population, our proposed sample size of 40 will be adequate for the main objective of this study. A post hoc power analysis will be conducted to assess if the sample size is appropriate to detect differences in a clinical population such as ABI.